This happens fairly regularly. I back the car out from the garage and while sitting on my driveway which slopes backward to the street I shift to Park waiting for the wife unit to join. When I try to shift out of Park, the stick feels locked then after applying about triple the force I ever had to for any other car, it releases with a "boom" sound. Seems to shift normally when not on an incline and I have no other problems with the tranny while driving. Anybody else have this or know if it is a sign of a pending problem?