2018 Sierra 1500 Transmission issues

[Calzoey]

4WD Crew Cab 8 speed transmission. 8500 miles. Transmission always feels like it’s trying to find what gear it should be in when cruising around 35 - 40 mph. Yesterday it started shuddering and felt like it was slipping constantly no matter what the speed. Researched on web and see a multitude of complaints as well as class action lawsuits being filed against GMC. I also saw where it was recommended from GMC to either replace fluid with lubegard or drain some fluid and use the lubegard as an additive. I’m looking for input from anyone who Is/has experienced this issue and how you had it resolved. Thank you.

[richard wysong]

Sounds like a torque converter issue, 35-40 is when it locks up. If it fails you will have to rebuild the transmission to repair the damage. If you replace it now with a billet  converter you may avoid that but it sounds like the damage may have already been done

[CamGTP]

I would not use anything other than the new Mobil 1 transmission fluid that is required for those trucks. If if not running the newest fluid available, that is the first thing I would be doing.

[JimCost2014]

Just like CamGTP said, if you are still on the factory fluid, swap it with the correct Mobil 1. You will get the same "warning signs" as if the TC were going bad when the factory transmission fluid begins to deteriorate. 

[ohed]

I had  the similar issue and after the application of Mobil1   the  problem returned. The  dealet  replaced  the torque converter (under warranty)   this  fixed it