The contact owns a 2019 GMC Sierra 1500. The contact stated that while driving at an undisclosed speed, the transmission unexpectedly hard downshifted. No warning lights were illuminated. The contact stated that the vehicle was hesitating while driving the rest of the drive. The vehicle was taken to the dealer; however, no cause for the failure was found. The dealer performed an 8-speed transmission fluid and filter replacement. The contact stated that the failure persisted. A month later, the contact stated that on a separate occasion, the transmission unexpectedly downshifted. No warning lights were illuminated. The vehicle was taken to the dealer; however, no cause for the failure was found. The contact stated that the failure persisted. The contact stated that a month later while her husband was driving on the freeway at an undisclosed speed, the engine seized and the rear-end locked and threw the driver into the steering wheel even though the seat belt was securely buckled. The contact stated that the transmission was stuck in drive(D), and the vehicle was unable to move forward. The driver shifted into reverse(R) and was able to pull off the freeway. The contact stated that the vehicle was then driven to an empty parking lot and left overnight. The vehicle was then picked up the following day and was driven to the dealer; however, no cause for the failure was found. The contact stated that the failure persisted. The manufacturer was notified of the failure. The contact