Just to further clarify, if you have a RWD or AWD vehicle in 'park' on an incline of say 5 degrees, and you jack up the rear end (being one of the either ends in your statement) with a wheeled jack, it is likely going to roll downhill. It is also very dangerous and should not be attempted.
However, that doesn't mean the transmission 'park' feature is missing or not working. It also doesn't mean that AWD doesn't have the same 'park' feature.
lol, NO PARK ON GM AWD SUV'S, AWD vehicles have no park instead it binds front & rear axles. still shows "park" in the cluster like normal it just doesn't park in the traditional sense. done with the matter, I was only posting this info for the OP in case they were not aware and thought perhaps they had lost park.
on a separate note I have broken the parking pawl on a non awd gm suv before among many other things
if you jack up your 2wd or 4wd gm suv (with an actual parking function) and it rolls away on the rear wheels then ya you have a problem, normally it should not budge, however a AWD gm suv will roll away, it might not so much if the parking brake is set but the parking brake does not hold nearly as much as parking would on a non awd.
also if you put a gm awd in park and lift up all 4 wheels front and rear will turn together in opposing directions NO PARK function.
but don't believe me, go try it for yourself........ i suggest you not stand in the direction of travel or just let natural selection take over.