Yyequipment

Final update: Dealer installed a new transmission valve body and referenced bulletin #21-NA-275 on the repair order. The bulletin states ABS event. Not sure why you would need to replace a transmission valve body for a ABS event. Anyhow we will see how it performs in the next couple of weeks.

Update: Dealer said they will be installing a new Transmission valve body covered under powertrain warranty. I asked the dealer what component within the valve body failed and he did not know. I also inquired as to what collateral damage was caused by transmission locking up at 75MPH and he said they could not find any. Not what I would expect from a Allison.

I am also experiencing the same issue right now with my work truck a 2020 Silverado 2500 Duramax with 82,000 miles and no modifications. Last week I was driving down the highway at 70 mph with a small trailer that has no brakes, I had the trailer tow feature as well as the exhaust brake on. I thought a strap had come loose and got under a tire causing the wheel to lock up or I had blown a tire. Very scary... everyone behind me slammed on their brakes and then about two hundred yards later it did it again. Both times I looked in the mirror and it the smoke appeared to be coming from the trailer, no brakes on the trailer so no possibility of that. I pulled over and both straps were tight and not damaged neither hub on the trailer was overheated and everything seemed to be fine. I slowed way down and it made it the 80 miles back home with no problems. I didn't no what to think and to be honest pretty much forgot about it over the Memorial day weekend. Tuesday comes around and I hook up a 20" cargo trailer I have with brakes and head out the 120 miles to make the same trip. About 90 percent of the way there at 70 MPH it does it again, locks up for maybe two or three seconds and then releases. Same exact feeling and sensation as the first time. Once again I slowed way down and turned the gain down on my controller to 0 and about ten miles down the road heading towards the dealership it locked up again and threw the tranny into some weird mode where it couldn't find a gear for about 5 seconds. Dealership said it would be at least a week for an appointment so I limped back home via the backroads at 45 mph and will try to get a service appointment here locally. I have never in almost 58 years of life experienced something like this happen with a relatively new vehicle. It is very dangerous not only for the operator but for the motoring public that happens to be around you when it happens.