01 suburban z71. Noticed slight movement forward on slight incline with vehicle in park and shut off. 175,000 miles runs great. Pulls trailer great.
How "slight"? If you are on a hill, brake on, put in Park, release brake, it may roll a couple inches, until the pawl catches. If you mean moved by it's self, say you saw it move unoccupied, be sure to set parking brake and chock wheels.