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What the posters here are feeling is not normal, unless the car was designed to disappoint and wear critical components early.. The fact that there are 6 pages of this concern here verifies it. If you are not experiencing it why post any comments against the members here that are? It is a definite real driveability problem. I was scurrying through a spirited right hand sweeping turn yesterday and it flared from 2 to 3 like I dropped it into neutral. Mines a 19 AWD with about 6000 miles on it.

Service manager drove it and stated there is something going on with the trans that is not right. Mechanic said cant figure it out, when it fails or gets worse so I can figure it out bring er back. Abeloff GMC Stroudsburg PA. Glad mines a lease but still not happy. When things get more back to normal i'll pursue it again and if I get a fix for the common man Ill share it here.

Other than that I am hands down done with GM products. Done. Done. Done. Both my full size GM pickups where also the worst almost undriveable trans programming ever. I thought my 16 Acadia was bad at 49800 miles on trade in, this 19 is worse. I'm looking to bail early (somehow) when things get somewhat back to normal.
 

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Hi, new to the forum! I am both happy to find Im not the only one having issues with my 2017 Denali, and saddened at the same time that it sounds like it is a problem they havent figured out how to fix. I have been to the local dealer (4) times. They've replaced upper & lower valve bodies, and now also TCM, flushed fluid, etc with no improvement.

Even worse for me, last visit it got hailed on so now I have a $2200 estimate for PDR for a vehicle that wouldn't have been at their facility to get hailed on had it not had all these trans issues since we bought on Feb 14 2020. Very frustrating to say the least. Oh and I've got the wheel clear coat peeling issue going on too.

This is a Certified Pre-Owned with 45k on it of which Im convinced they did not "refinish & renew" during their certification process and instead just slapped the certification on it to help sell it.
 

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Hi, welcome. Yeah no ones fixing this. In my opinion its a design oversight that likely COULD be fixed via updated Gm or aftermarket programming. As you stated even with fixes and flushes its still there, and in my case at the most random times.

On another note the CPO thing really just gives you a more warm fuzzy feeling that maybe, just maybe, someone went through it after it met the CPO qualifications. I've bought CPO Mercedes cars in the past and some have definitely not been gone through as they should have been so its not a brand thing there, just either the dealership or individual mechanic himself.

Just so you know I've had this issue in my current 2019 and also my 2016 Denali (traded) and after multiple flushes it got way better for a few thousand miles then crept back in full fledged. Shame because I really like this model other than that and the noisy headliner clips around the sunroof, of which I bought a box of 20 and changed about 12 of them carefully "insulating" them with tape.

You know what? It still makes noise.The trans?? Eh, I guess live with it if you can or look to trade in on something else. Trouble is now that you know it does it, when it does shift flare it's going to irritate you. Mines a lease and it burns my tail when it does it.
 

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Im going to take it back to them one last time to see what they want to do, even though I know its probably not going to be fixed with whatever they do - best case scenario they maybe replace the trans and I have the peace of mind knowing that at 46k on the clock I got a new trans. Other thing is that I may pursue what maggie(magtuning) was talking about and try to see if I can mess with the shift tables it hptuners to change what it does. We will see. SIGH
 

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I'm thinking this should be on a new thread, but likely the moderator will combine them anyway...?
I wonder if there's any common ground between the vehicles. Mine is a '19, pretty sure I saw others of differing years however. Scratch that.
Mine; final assembly in Spring Hill TN. Are they all assembled there? Looks like it, strike 2.
I do think this is not mechanical. More likely a programming issue. Does the BCM control the shifting? Perhaps all of the vehicles in question sourced their BCM's from a different supplier?
I don't know, but it would be nice to find out.
 

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Im going to take it back to them one last time to see what they want to do, even though I know its probably not going to be fixed with whatever they do - best case scenario they maybe replace the trans and I have the peace of mind knowing that at 46k on the clock I got a new trans. Other thing is that I may pursue what maggie(magtuning) was talking about and try to see if I can mess with the shift tables it hptuners to change what it does. We will see. SIGH
Let us know if you do play with the tables...
 

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I do think this is not mechanical. More likely a programming issue. Does the BCM control the shifting? Perhaps all of the vehicles in question sourced their BCM's from a different supplier?
I don't know, but it would be nice to find out.
Even though my '18 does not have this issue, I suspect it is a software problem. Not sure why dealer techs keep throwing in new parts hoping to resolve the issue.
 

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Even though my '18 does not have this issue, I suspect it is a software problem. Not sure why dealer techs keep throwing in new parts hoping to resolve the issue.
People here have had valve body replacements, full tranny replacements... yet still the problem remains.
I think it's maybe the learning curve of the vehicle. In my case, I have 3 speed bumps on the street after I exit my street. Each one is just at that "2-3 have to lay off the gas for the next bump" distance. Am I training it to shift this way partly? Maybe.
 

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People here have had valve body replacements, full tranny replacements... yet still the problem remains.
I think it's maybe the learning curve of the vehicle. In my case, I have 3 speed bumps on the street after I exit my street. Each one is just at that "2-3 have to lay off the gas for the next bump" distance. Am I training it to shift this way partly? Maybe.
As you stated, the fact that it remains even after new hard parts and in some cases entire new transmissions, would indicate a constant between the two (or more) attempts is the culprit. Even after a trans control module what good is it if the tuning in that module is the same as the prior one. If you look to the successful fix as claimed at this point,it would be in the tuning as (I believe Maggie ?) has indicated. If that were available widespread through one or any source, I think we would be done and moved on from this issue.

One thing that can't be disputed by anyone is that so many operators of this vehicle acknowledge it and I would hazard a guess not all come here looking for answers. Some just chalk it to one of life's less than adequate products and don't have the time or inclination to look for a fix, so I would bet the problem is more widespread than what we know. I also notice recently even some of the downshifts suck. I feel them too much. This transmission is not smooth many times.

Bottom line IMO: it's poor engineering and I take pride in my work and if I were responsible for this I would feel compelled to fix it. My philosophy on a given task is "Take the high road,there's less traffic there". Don't just say oh well who gives a crap and move on. But I guess, hey that's GM for us. Last one for me, No doubt.
 

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I do believe the tuner guy probably has the ability to do so, but unlikely I'd tackle that while under warranty. After... probably. He did post approximately the steps he made to rid the tranny of this.
And I completely agree. If there are 5-10 here, there are plenty more out there that don't hit auto forums.
Always... take the high road! (y)
 

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I confirm it’s 100% software related. New transmission and torque converter, multiple flushes and reflashes. Still 2-3 flare at time albeit better than before. If all the hardware was replaced leaves me no choice but to confidently say software. Very odd.
 

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I confirm it’s 100% software related. New transmission and torque converter, multiple flushes and reflashes. Still 2-3 flare at time albeit better than before. If all the hardware was replaced leaves me no choice but to confidently say software. Very odd.
Are you quite light on the pedal when it's cold; 2-3 shift at a lower RPM?
I am seriously starting to think it is driver (tranny learning curve) related. Me leaving my house every day:
-Pull out of driveway, go down street. Street is 6-7 houses to where I turn, so I really barely hit the 2-3 shift.
-Turn left onto next street which has 3 speed bumps over 4 short blocks (it's a cross street, so some people use it to save a few minutes). Between each speed bump, again, it barely gets to the 2-3 shift. That's 4 short blocks to first single yellow lined street. That's also 4 times that I "teach" my tranny how to shift, yes?
-Hit next street and turn right. I'm now finally on a stretch where my car can actually shift from 2nd to 3rd fully. The remainder of the way is regular roads.
So maybe the learning nature of the tranny is using my every day leaving the house light 2-3 shift, and slowing it down.
Anyone, thoughts?
Anyone else who has this problem, have a daily routine that is similar?
 

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You may be right about the learning curve. But as I'm sure we agree if you need to stop and go somewhat irregularly, the damn car should be able to compensate in another way besides a slip or delayed shift. Bad engineering if that's the case. Upon (GM) recognition of this customer concern, refusal to come out with an update or fix? Well that's just bad ethics.
 

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Are you quite light on the pedal when it's cold; 2-3 shift at a lower RPM?
I am seriously starting to think it is driver (tranny learning curve) related. Me leaving my house every day:
-Pull out of driveway, go down street. Street is 6-7 houses to where I turn, so I really barely hit the 2-3 shift.
-Turn left onto next street which has 3 speed bumps over 4 short blocks (it's a cross street, so some people use it to save a few minutes). Between each speed bump, again, it barely gets to the 2-3 shift. That's 4 short blocks to first single yellow lined street. That's also 4 times that I "teach" my tranny how to shift, yes?
-Hit next street and turn right. I'm now finally on a stretch where my car can actually shift from 2nd to 3rd fully. The remainder of the way is regular roads.
So maybe the learning nature of the tranny is using my every day leaving the house light 2-3 shift, and slowing it down.
Anyone, thoughts?
Anyone else who has this problem, have a daily routine that is similar?
I live in an incredibly similar situation complete with speed humps but I’m not convinced that’s the issue.

Heavy throttle = no issues. Babying throttle = no issues. Regular driving = happens all the time. We’ve had the car for a year and learned to drive around the issue somewhat but sometimes inevitable.

I wish they would just offer a software fix. Have you noticed from a rolling “stop”, maybe 15mph the 2-3 shift is so smooth you can barely even notice it. But if I actually stop and then go, the 2-3 shift is terrible. Wild.

Mine also vibrates at idle with small tremors that is driving me nuts. Started thinking that is injector related but that’s for another thread lol. Love the car despite the issues but they drive me insane.
 

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hogdad; indeed this is a problem, I'm just trying to figure out why it happens.
dsgvw; interesting on the similar driving conditions. I have the same; heavy throttle/higher RPM it shifts quite rapidly. Lower is also fine. What I wonder is that low/mid throttle when it lags, is also how we apply over those speed bump type driving, so perhaps we are teaching it for that throttle application range. Rolling shift is smooth for sure, almost not there.
 

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I was actually able to reproduce it on a right turn if I drove in the same manner/same style as the left turn when it always does it - a long sweeping right turn with light acceleration - Service manager asked for me to bring it back today so they could log some more driving and submit another TAC case to the engineers & see what they want to do next. Not feeling confident about whatever they think they need to fix next, since I am on the same page with everyone here in thinking that it is a software issue, not a hard parts issue. Maybe they'll give me a new trans! lol - hoping for the best
 

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I'm thinking this should be on a new thread, but likely the moderator will combine them anyway...?
I wonder if there's any common ground between the vehicles. Mine is a '19, pretty sure I saw others of differing years however. Scratch that.
Mine; final assembly in Spring Hill TN. Are they all assembled there? Looks like it, strike 2.
I do think this is not mechanical. More likely a programming issue. Does the BCM control the shifting? Perhaps all of the vehicles in question sourced their BCM's from a different supplier?
I don't know, but it would be nice to find out.
Mine is a 2019 SLT FWD also. I don't really notice an exact thing I could call "flare".
But I will say that sometimes I notice erratic shift behavior. Like if you start out from a stop slow a bit, then give it some gas pedal. It will then stay in whatever gear (2nd) for a longer time before it will shift again. it kind of lurches at times.
As much as the 8L45 and 8L90 eight speed GM transmissions get critiqued, the one in my 2017 Colorado is much smoother than the Acadia.
Anyway, I'm thinking the Acadia is more a programming issue that could be worked out. But likely won't be for certification reasons of EPA or some similar thing.
Probably why a tune seems to correct it for those who choose that route.
 

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If only someone made a software tune/upgrade for the trans that we could load via the obd2 port like my GTI. Ohh well, wishful thinking anyways.
I've even tried putting the Transmission Mode dial in Sport Mode and that doesn't really seem to help any.
 
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