The contact owns a 2015 GMC Yukon XL. The contact stated while driving at an undisclosed speed, the transmission jolted before the vehicle accelerated as intended while depressing the accelerator pedal. No warning light was illuminated. The contact stated that an independent mechanic was contacted; however, the vehicle was not taken to be diagnosed. The contact stated that unknown repairs were performed on the vehicle, but the failure persisted. The manufacturer was not made aware of the failure. The vehicle remained at the residence and had not been driven since the failure. The failure mileage was unknown.