2017 GMC SIERRA Power Trainautomatic Transmission Problems

The contact owns a 2017 GMC Sierra. The contact stated while driving at various speeds, the transmission inadvertently shifted from high to low gears and the RPMs revved up. There was no warning light illuminated. The vehicle was taken to the dealer where the failure could not be duplicated. However, the failure recurred while driving. The vehicle was then taken back to the dealer where it was diagnosed that the valve body, the clutch, the piston, and the transmission plates needed to be replaced. The vehicle was repaired, however, the failure persisted. The contact stated that while driving and an undisclosed speed, the transmission was shifting hard into a lower gear, then into third gear without warning. The vehicle was taken back to the dealer but was not repaired. The manufacturer was not notified of the failure. The failure mileage was approximately 60,000.