Car Accelerates On Its Own problems of the 2012 Dodge Ram 1500

Upon selecting transmission "d" option instrument panel indicated "6", drove to barn for horse feed. Needing to back up to fence, to disperse feed, transmisson selection of "r" was necessary. Using the brake pedal to regulate speed and no usage of accelerator pedal (as automatic transmisson vehicles will generally motivate when gear selection is initiated) "sudden acceleration" occurred causing damage to tailgate which was down. Brake pedal was pressed and vehicle was stopped. With brake pedal depressed transmisson selection "d" was initiated, in order to investigate damage, and once again with brake pedal used to regulate speed and no usage of accelerator pedal "sudden acceleration" was again encountered. Brake pedal was again depressed which stopped vehicle. No further occurrances were encountered that day. Weather was sunny and cool, high 40's, with dry conditions.