On July 1, 2023, I had the vehicle parked on an incline with a trailer attached to the vehicle. The vehicle was in Park and the Parking Brake was set. As I attempted to unload the trailer, the vehicle started to move and rolled down the incline. I was on the trailer and was moving with the vehicle, I could have been injured but fortunately the vehicle rolled into a pile of topsoil before it could pick up too much speed. However, both the vehicle and trailer were damaged My safety was put at risk as the vehicle was moving without anyone in it. This occurred in my driveway but could have happened on a busy street. I still own the vehicle and it is available for inspection. There were no indications, warning lamps, etc. that would have notified me of the impending failure. I contacted Ford and they have been of little help. It took them 2-1/2 months to get me scheduled to have one of their field service engineers to inspect the vehicle. I was not allowed to talk to the field service engineer and that person did not attempt to duplicate the conditions which caused the failure. The report from Ford to me said they inspected the vehicle on a lift. They said they could not find a problem and said they will take no further action. They have been extremely uncooperative and do not seem the least concerned about the safety of the vehicle. I am concerned that the problem will recur and cause significant damage or injury so I take precautions whenever I park it.