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I haven't seen any new discussions lately regarding the transmission shifting.

I have an 08 SLT2 manufactured and delivered the end of February 08. I am not very pleased with the shifting pattern, and wondered if it is normal, or if I have a problem.

The transmission does fine in town. When I get out on the Interstate, at 70-75 MPH, it is traveling along fine in 6th gear at 1800 to 1900 rpm until we get to a grade up. The car begins to lose speed, then appears to shift down all the way to 4th, jumping 1000 rpm to 2800 to 2900 rpm. It then goes back to 6th and drops back to 1800-1900 rpm. Once in a while it drops to about 2600-2700 rpm for a minute, like it hits 5th, but only stays a second or two. This happens both with the cruise on, and also if I am trying to accelerate lightly to keep a constant speed.

On the state highways, traveling 50-60 mph, it does about the same thing, bogging down, dropping all the way from 6th to 4th, jumping 900 to 1000 rpm, then going back to 6th while it drops 900 to 1000 rpm. It does seem to hit 5th a little more at this speed than the Interstate speeds, but still only stays there a few seconds, and only on the way back up to 6th, not on the way down to 4th.

Is this all normal? Why does it not downshift more to 5th when losing speed instead of going all the way to 4th and jumping 1000 rpm's? I don't drive it hard, and don't use cruise control on hilly roads trying to avoid harsh downshifting. However, I can't seem to avoid the bogging down and the 1000 rpm jumps.

Do you think my vehicle has a problem, or is this the nature of the Lamda platform vehicles.
 

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It's likely the nature of the beast. I wonder if you are really dropping into 4th. You might want to do a test and put the shifter into L and change from 6th, to 5th, to 4th and get a feel for what the RPMs are in each gear at 70 mph. The torque converter locking in and out will also change the RPMs so it could be that your initial jump in RPMs that you call 4th may really be 5th with the torque converter also unlocking, and it could be that mid range RPM you see is 5th gear with the torque converter locked in. Do some testing and see.

How many miles are on your car? With mine, it took about 1000 miles before this condition mellowed out and was much less noticeable. Some say the transmission learns and the computer adjusts, and some say the car breaks in. I don't know if either of those happened, or if I just got accustomed to it, but I do know I no longer notice it dramatically shifting as I travel at 72 mph. It still shifts down up the grades, just not as often.
 

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rakfire,

Check out this thread for a transmission update that may address your problem:

http://www.acadiaforum.net/forum/index.php?topic=3576.0

PIP4378: Busy Shift With Cruise - keywords 07 08 5-6 6-5 6t70 6t75 busy control downshift ecm mh2 mh4 mh6 my9 r1 r2 r3 seq shift tcm upshift v1 v2 v3 - (Mar 28, 2008)


Like GAR, I don't seem to notice it now as much as when our Acadia was new, even without the above update.
 

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I'm in total agreement with RAKFIRE, my March 2008 built Acadia does all the same things. Hopefully it smoothes out like GAR mentions.

Other than that, I love the darn thing!
 
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