Jim Roach

This has happen 6 times in 18 months and did it again this weekend. The first occurrence was when the truck was 4 months old, 2018 Sierra Denali Ultimate 6.3. It was a cool morning in October ( about 50 degrees F). The engine was warmed up for about 10 minutes. I approached a stop sign and it felt like the brakes suddenly faded and I slid half way into the intersection when I realized the tach was at 3,000 with my foot on the brake. As I continued on, the operation returned to normal. Outside temperature seems have something to do with it as it has never done this in the hot Dallas Summers. The second time was in a parking lot after leaving the truck in cool weather at a hardware store for about 20 minutes. I started up, back out of the spot and at the first stop the engine revved to about 3,000 while I was braking. This time I slid the transmission into Neutral while holding the brake and the RPMs went to 5,000 and held there. I revved the engine a few time and the engine went back to idle and performed normally after that. This happened thee more time that winter. Last weekend, the first cold weather we have had for awhile and after driving the truck for 45 minutes, pulled up to a farm gate and I put the truck in Park while my buddy jumped out to open the gate. When I placed the the truck back in Drive with my foot on the brake, the engine revved again to about 3500 and half drug me through the gate while holding the brake firmly. I placed the truck in neutral and again the RPMS went to about 5000 and held. I fanned the accelerator a few times and the engine returned to normal idle. When this happens it will not repeat for weeks or months. The Dealer of coarse cannot replicate. I am a former dealer and technician so I don't panic when this happens as I know the brakes will ultimately hold and shifting to neutral will stop the forward progress. I will not let my wife or anyone else drive the truck until someone figures this out. I now have 28,000 miles on the truck. Any ideas?