I PARKED THE TRUCK, WITH THE MOTOR RUNNING AND PUT THE AUTOMATIC TRANSMISSION IN PARK. I LEFT THE TRUCK TO MAIL SOME LETTERS. I WAS GONE LESS THAN A MINUTE AND WHEN I RETURNED TO THE TRUCK, IT WAS ACROSS THE STREET AND UP AGAINST A LARGE TREE. I KNOW I HAD PUT THE TRUCK IN PARK, BECAUSE IT WAS NOT MOVING WHEN I GOT OUT OF THE TRUCK. I HAVE TWO BAD KNEES AND I GET OUT OF THE TRUCK SLOWLY.