I read somewhere that for A/T cars, the proper way to park uphill/ downhill is to put car in neutral while stepping on the brakes then put the hand brake up. (make sure that you crank it up to the maximum) Slowly let go of the brake pedal and make sure the hand brake's holding up. Switch off the engine then shift to park. After doing this procedure, haven't had any problems with shifting from park to reverse or drive when parked uphill/ downhill. Although i might be wrong.. let's wait for the expert to shed some light on this..