Get a code reader and see if there are any transmission codes stored. Have you ever changed the transmission fluid? These E's are hard on all fluids. Easy DIY job to get out five quarts, refill drive a week and do it again. You will get out most of it this way. I would avoid a flush. They do have TECHM issues "transmission control module", which usually is one or multiple switches in the control module. There are four total. could be one or two going bad. That repair is about $1200 to $1500. There is a self repair that is a 5-7 hour job for the intermediate or better mechanic to fix them, takes 5-7 hours on average. Youtube is your friend here along with the Acadia forum. Check codes, if no codes change fluid. Could also be a misfire giving you the feeling. Get the engine codes read also. Good luck, please post back results.

 

My ‘12 (99k Miles) was experiencing similar problems to yours on a recent trip to Michigan. My issues were gears 2-4, it would either shift way late at highway speed or the tach would bounce 2-300 rpm when at a steady speed going up a slight incline. Nursed it home 11 hours and had my local dealer diagnose the issue as a bad torque converter. Apparently quite a few of the ‘12’s have had this issue. $2,500 later it’s good as new...I say this b/c I’ve had several issues within the last 1-2 years that make me think it’s time to dump it. FYI the trans fluid had been changed recently and had no engine codes.

 

My only trans problem on my 2012 is the trans shudders occasionally (going up slight inclines w/light acceleration) darn sure it is the torque convertor going so I add Lubeguard ShudderFix and it works for a few months. I'm just gonna keep doing that til I get rid of the car or need a new Torque Convertor. No codes 140K

 

My 09 had 73K miles when I had to have the transmission rebuilt about a month ago (absolutely no codes). At about 36K miles, I had a slipping shifting going into 3rd and 5th. The dealer didn't find the 3-5-R waveplate broken, but other stuff was bent. The TECM was replaced and reprogrammed. It all worked fine until about 72K miles, when I noticed a 2 second delay going to drive. This got worse, then I had 2 instances where the vehicle wouldn't shift past 2nd gear. I had to shut it down then restart for the vehicle to drive normally. Since my family rides in this car, the second time this happened (not shifting out of 2nd gear) I took it to a specialty transmission repair shop. I figured it was the TECM, but since it had only about 37K miles on it I thought it would last a bit longer. Because this shop wanted to do the job right, the only way they could ensure it would be fixed was to tear it open. They found burnt clutches, and replaced the torque converter, seals, clutches, wave plates, etc. - all the wearable items - using a master rebuilt kit. The transmission shifts like new again, but they did say it was too soon to see these kinds of issues. This job was expensive, but I needed it to be safe for my family and it was cheaper than buying a new car. Keep in mind I had all these issues even though I changed my transmission fluid (drain/refill 2x) every 25,000 miles. If you have a 2014 or newer (Generation 2) then probably most of the problems have been worked out. But those of us with Generation 1 of the 6T75 have a crappy transmission. Ford used a similar version of the transmission but they have fewer issues most likely due to better parts used.

Bottom line: Seems like GM's cost accounts just won't let the company build a reliable car anymore. Sorry to say, after this experience I won't be buying another GM car again. My 09 Enclave has been in the shop for more issues than all the other cars I have owned - combined. I cannot believe how a company like GM can build such as useful vehicle, but ruin the ownership experience for its customers due to very poor reliability. But I guess for GM's "top brass" it's all about profit. That's all good, but I'll a be looking elsewhere for my next vehicle. Thanks GM!