I was on a gravel road that was nearly level to very slightly up hill. Upon passing some branches that were hanging partially over the road, I decided to trim them so they would not cause me trouble on my way back. I put vehicle in REVERSE and backed up maybe 20', shifted into PARK, got out (left vehicle running), opened the rear door to get clippers and closed it. Walked to the bush maybe 15' to rear of vehicle and clipped a couple small branches and I suddenly heard gravel noise and looked up to see my truck moving FORWARD on its own. I immediately ran after it and it veered left, left the road, proceeded down a hill and crashed into a small tree! This vehicle was a part of the Nissan Parking Pawl recall. I had the needed repairs done by Nissan on April 11th 2023. The vehicle malfunctioned!! Problem has not been reproduced. There has been no inspection by anyone at this time. There were no warnings.