I have a 2018 GMC Sierra 1500 w/8 Speed Transmission and it has been the worst shifting vehicle I have ever owned in 50 years of driving. The transmission bangs, clunks, slams into gears and at times misses shifts where it feels like it is in neutral. I have taken it to the dealer (4) times while under warranty and they continuously state noting is wrong. They reset the transmission, whatever that means, and it helps for about 5000 miles and the issue starts again. Please, do you have any ideas as to what could be wrong with this transmission? My truck just turn 60,000 miles and it seems the dealer just can't fix this problem. I purchased this truck new and I have made certain all the recommend services have been preformed on schedule.
Join the club.
https://gmauthority.com/blog/2021/01/class-action-gm-eight-speed-transmission-lawsuit-hits-a-snag/
Your transmission will gradually self destruct, and there isn't a damn thing you can do about it, unfortunately.
Maybe take advantage of the high used car prices right now and sell it.
See below: you are not alone, that GM designed 8-speed AT (8L90) is one of the worst ones made by GM, and I consider it a top deal breaker in owning a modern GM product. How often are you getting the transmission fluid changed?
There is a new fluid GM came out with in 2019 to address some of the transmission issues (primarily with torque converter). They did a “triple flush” with this fluid for some C7 Corvette owners and it seemed to help them. But how long it lasts for - who knows? Have you had the dealer try it in your scenario? See below:
https://gm-techlink.com/?p=11127
