8L90 M5U Hydra-Matic automatic transmission clunking and lunging

[alejalva]

I have a 2015 All Terrain with the problematic 8 speed transmissions. The dealer has been great but they have replaced the torque converter, reprogrammed it 4 times and just installed a new valve body. They odd thing is it does the same exact thing. I'm asking for a new transmission and TCM. My question is, is there a fix? My next step is to Lemmon law the truck and get a replacement truck or just go with a different brand. If someone has gotten their transmission fixed please let me know what they did to fix it so I can pass it along to the dealer. Thanks for the help!

 

 

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[diyer2]

To me they have replaced the main mechanical parts so far and it didn't work. I would push for new trans and TCM.

Good Luck

[True North Truckin]

I would agree and say try for a replacement trans I have owned two trucks with the 8L90 including my current 2016 Silverado and although I found both 8-Speed trucks did shift firmer then my 2015 6-Speed truck neither exhibited any kind off noise or lugging, hopefully they get you issue resolved because I love the 8 gears I found it made a drastic improvement in my fuel economy and towing over the older 6-speed.

[alejalva]

Quick update. GM agreed to replace the transmission which includes the TCM. They tried to say the bigger tires could have been an issue. I called BS! I just got those tires a 5 days ago and the problem has been there for at least 2 months! I thought about not getting the new tires until after I get this whole issue resolved but with the bad weather and the bald tires i needed to get them. I also went from a 275/55 to a 275/60. Not like I went big time over sized. But they said due to the bigger tires I might have a harder down shift. Which I call BS too because I've done it to other GM trucks and never had theses types of issues. I just hope this takes care of the problem and I can move on.

 

 

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[alejalva]

Picked up my truck with the new transmission and it's running so much better. I was told GM is working on new software for the transmissions in order to fix a lot of the problems. I'll keep everyone updated if I hear anything else.

 

 

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[Timmyz]

Any info on that software? I bought a 2016 in January and it has been to the shop over and over for the banging into 2nd gear and no fix yet