The contact owns a 2014 GMC Sierra 1500. The contact stated that while driving on several occasions at speeds of approximately 35 MPH, the transmission shifted abnormally, and the vehicle started vibrating. Additionally, the contact stated that while driving at speeds of 65 MPH and higher, the failure worsened. The vehicle was not diagnosed or repaired. The manufacturer was notified of the failure. The failure mileage was approximately 146,000.