Torque Lock

Best way to do things is to hold the car with the brake, shift into park and then engage the parking brake. I think the slope of the "slight incline" is putting too much weight on the pin that engages when putting the car in park. This is not a "torque lock" but, instead, a mechanical condition created by the sequence of how how you engaged the parking brake and "Park" on the incline. Only thing I can think of is to take the parking brake off and then trying to push or pull the car forward an inch or two. This should take the pressure of the transmission pin that engages "Park". At the same time try to put the trans in neutral. An alternative would be to jack up the drive wheel corner and try to rotate the tire slightly in the forward direction and put the car in neutral. If these tricks don't work or you cant do them, then call for assistance from a service company. Good luck.