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Discussion Starter · #1 ·
Does anyone else have a lot of (excessive) shifting going on when the have the cruise control engaged (around 60-65 mph)? Driving the same roads with no cruise control and there is not nearly as much downshifting going on (even when I hold the same speed)? Sometime a single small incline will generate two or more downshift/upshift cycles. ???
 

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Somebody has to ask.....Did you get the May 8th flash done?
 

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I use my cruise control daily, usually around 55mph, but also often enough at 60 or 65mph. I haven't noticed any excessive shifting though.

Do you have the May 8th transmission update?

I will try to pay closer attention to the shifting on my way home tonight and report back about the shifting.
 

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May 8th optional update fixes that.
 

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canyonblue737 said:
May 8th optional update fixes that.
Maybe folks ought to add that tidbit of info to their signature lines so others know if they have or not.
 

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Okie doke. On my drive home, I tested out the cruise control at both 60 and 65 mph. On flat surface, and uphill/downhill surface (okay not really HILLS... this is Illinois, but definitely not flat). The RPMs hardly changed. The transmission did not shift erratically, in fact, I don't think it shifted at all given that the RPMs were fairly constant the entire time it was in cruise. Even when it accelerated for an incline, it did so ever-so slightly and gradually.

I'd venture to say that if you haven't gotten the May 8th update already, it will fix the issue you are experiencing.
 

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tm59 said:
Does anyone else have a lot of (excessive) shifting going on when the have the cruise control engaged (around 60-65 mph)? Driving the same roads with no cruise control and there is not nearly as much downshifting going on (even when I hold the same speed)? Sometime a single small incline will generate two or more downshift/upshift cycles. ???
Here's a decent thread on the subject (one of many) from the Encalve forum. Reason I target this one is that towards the end of the thread one of the GM transmission programmers addresses the fact that this latest tranny update does indeed fix that constant shifting issue while in cruise at high speeds.

http://www.enclaveforum.net/index.php?topic=3134.msg44521;topicseen#new
 

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Discussion Starter · #8 ·
I had the May 8th update, but I thought that was about flat spots (shift points) in mild acceleration. At least that's how it was explained to me. I will check out the enclave link as I thought I remembered something about it there. I have no shift problems without cruise, but engage the cruise and it's shift happy.
 

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I had the May 8 update performed, and I still get a lot of 5-6-5-6 shifting on hills with cruise set. I think this behavior is a possible drawback of multi-speed (six or more) transmissions that are programmed for economy.

Perhaps the transmission would be more enjoyable (if not more economical) if it downshifted quicker on hills, and held 5th long enough to crest the hill. I think it requires too much throttle to trigger the downshift, and then you have more throttle than needed in the lower gear - but easing off triggers an upshift, repeating the cycle.

I drove a Mitsubishi Galant rental car recently and was suprised by its easy, smooth performance on the highway. No busy shifting to maintain speed. This was a basic car: 2.4L four cylinder, 160hp, four speed auto. It may weigh 1300 lbs less than my Acadia, but the Acadia still has a better power-to-weight ratio. I think the difference is the gearing - the four speed in the Galant probably keeps the engine running in the powerband while the Acadia, with its extreme overdrive, requires a downshift to get there.
 

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Discussion Starter · #10 ·
I would also be happy if it downshifted to 5th and held that gear to maintain speed. But it goes to 5th briefly, then to 4th to build speed quickly, then after a brief moment in 5th its up to 6th again. This cycle is repeated twice on small inclines and three times on longer (but mild) grades. Maybe I should get the service tech in for a ride. I do agree with gmc4me.
 

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I did notice that on the road trip I just took. However, I noticed that on signifigant grades, it would take a while to downshift to 5 (usually dropping about 3-5mph) and the it would hold it. The only problem after that is that it would not shift back into 6. I either had to start a descent, or tap the brakes to turn off the cruise and it would shift up, and then turn the cruise on again. The main problem I found was on "rolling hills" where it goes up and down and up and down, not any signifigant grade, just while driving over farm land and stuff. By the time I reached the crest of the hill, it would downshift, then would upshift suddenly because we were going downhill again. It made for some jerky driving.

The main fix I have for this, either downshift to 5 and keep it there (which when not on signifigant grades, such as rolling hills kills mileage) or, listen GM, MORE POWER! That should fix anything. But, then again, mileage would suffer.

And yes, I did have the crazy (5) 8
 

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Discussion Starter · #12 ·
Could it be that it is not downshifting quickly enough? If it holds 6th too long, speed drops too much, too much throttle makes it down shift abruptly, 6th, to 5th, to 4th; which is too much torque so it cycles back up through 5th to 6th quickly ?? :confused:
 

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interesting... I just noticed this today as well....

so is this just a flash update that needs to get done at the dealership?
 

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tm59 said:
Could it be that it is not downshifting quickly enough? If it holds 6th too long, speed drops too much, too much throttle makes it down shift abruptly, 6th, to 5th, to 4th; which is too much torque so it cycles back up through 5th to 6th quickly ?? :confused:
That is a part of it. I have the May update and it is certainly improved, but there is no way around the fact that for economy reasons, it has been given a 6th gear that it simply does not have the torque to pull at highway speeds on anything but level road. A slightly shorter rear end gear would help the issue significantly but it might give up a mpg in the process. Even the latest direct injection engine update and trans combo in the '09 (in a Traverse) is significantly criticized in the latest Car and Driver for its "reluctant and indecisive" transmission. Its the price paid for squeezing the very last mpg out of the 5000 lb beast.
 

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I like the shifting in my 09 way better than my brothers 08 MB ML350.
 

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bseemore said:
canyonblue737 said:
May 8th optional update fixes that.
Maybe folks ought to add that tidbit of info to their signature lines so others know if they have or not.
Great Idea. And done!!
 

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07 SLT AWD, have had all of the fixes but find it easiest to just forget the cruise control. Recently drove the 09 version, and found it to be significantly better. The salesman wasn't sure, but thinks the gear ratio was tweaked. Am at 30,000 miles now, so may consider the '10 model.
 

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oralee said:
07 SLT AWD, have had all of the fixes but find it easiest to just forget the cruise control. Recently drove the 09 version, and found it to be significantly better. The salesman wasn't sure, but thinks the gear ratio was tweaked. Am at 30,000 miles now, so may consider the '10 model.
GM Powertrain lists all gear ratios as the same 08 vs. 09, but lzwhb2 posted that the 09 transmission programing is significantly different to go along with the DI engine.

I have noticed that there is significantly less shifting on the highway after the May 8th update was performed.
 

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With our May 8th tranny update, w cruise on, tranny shifts normally. It will make a heavier difference if a head wind w some hilly terrain producing more shifting. Lots a variables to think of with sensitivity in 5th and 6th.
Jet stream moves easterly...............
 
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