joeidaho

Update: I took the truck in on Monday and they kept it Tuesday to run a series of tests. No faults found. They couldn't duplicate the issue so I was allowed to take the truck back that evening. Yesterday (Wednesday) I am driving the truck down another highway doing about 55 and Slam!!! Brakes lock up!!! A motorhome behind me went off in to the ditch and about took out a fence. Luckily he and his wife were fine with no serious issues. I pulled off to the side and put the truck in park. This time, no trailer. Because I wasn't pulling anything, the truck almost came to a complete stop thus why the motor home about completely wrecked. Now - I did notice that this only occurs when I hit the acceleration and the transmission shifts down for more torque around the 50-55 mark. I slowly crawl the 8 miles back to the service center and now my truck is in jail. They are logging a ticket with the GM engineers and have all but certainly figured it's a transmission issue. No aftermarket modifications on the truck. Only a new air filter and tires. I took pictures of the skid marks on multiple areas to give verification. More to come. . . . .

I have a 2020 AT4 2500 Diesel with 37600 miles on it. Just under 2 weeks ago I was hauling my boat to the lake when the back truck brakes completely locked causing the vehicles behind me to veer off in to the side lanes to avoid rear ending the boat. I thought it was the boat trailer because the smoke coming off the back tires. I went another 200 yards and the truck did it again. This time everyone was back way way behind me. I couldn't pull over due to guard rails so I puttered up to the closest turn off and looked everything over. I disconnected the boat and made sure the brake away wasn't hung up and hooked it all back up again. I pulled out and went another 1/4 of a mile and it locked up again. This time I noticed the truck flashing the N for Neutral and the truck wouldn't go forward. So I had to put it in Neutral and then back to Drive so it would move forward again. I pulled over and disconnected all the hydraulics on the boat brakes and went on my way. Great weekend boating and no problem. On my way home, about a mile from the house the brakes lock up again; again causing all the vehicles behind me to slam on their brakes and go all over the place. Now, I had already called to make an appt for the trailer to get serviced. It was Sunday so I had to limp it home. Because I disconnected every logical part of the boat brake system I assumed no more issue. When I get home and I completely voided the brakes on the trailer of all fluid and took it to the boat dealer for service. The boat is new and this was the second time I towed it so I assumed it was some kind of anomaly with the boat trailer. Today I was pulling a fully loaded enclosed trailer and the truck locked the brakes again going 60 on a highway and all the vehicles behind me went to the sides and hurried around me to avoid a collision. Fortunately I was only a few hundred yards from my destination so I disconnected the trailer and took the truck to the closest service center. They have me scheduled to have it inspected tomorrow. I'm putting this on here so everyone can have the seed planted if there is some kind of computer glitch or something that comes up once the vehicle hits a certain mile mark etc. I honestly don't know but I have a fleet of other trucks for my construction business and this is the first GMC I have ever owned. I love the power and pulling capability but I would assume not many of you owners have reached this mile mark yet. But also to see if anyone else has had a similar issue. I'll keep everyone posted when I know more.