VEHICLE WAS PULLED 3/4 INTO THE GARAGE WITH THE BACK WHEELS ON THE APPROACH OF THE DRIVEWAY. VEHICLE WAS PUT INTO PARK AND SHUT OFF. I RETURNED TO THE GARAGE 10 MINUTES LATER TO FIND THE VEHICLE HAD ROLLED DOWN THE DRIVEWAY, STRIKING A TREE CAUSING SIGNIFICANT DAMAGE. VEHICLE WAS FOUND TO BE IN PARK AND STARTED UP WITHOUT ANY PROBLEMS. IN THE LAST COUPLE OF DAYS I HAVE NOTICED INCONSISTENCY WITH THE VEHICLE'S SHIFTER WHEN PLACING IT IN PARK. I HAVE SEEN IT GET HUNG UP BETWEEN REVERSE AND PARK. THIS IS A BRAND NEW FLEET VEHICLE WITH 1049 CURRENT MILES. IT JUST WENT INTO SERVICE ON JULY 5TH.