Suburban difficulty shifting into gear on hill

Our 2003 2 wheel drive suburban is having difficulty shifting into gear when we start the car if we are on a hill. What is the liekly cause?

I’ve seen this a lot with cars and trucks that don’t have the parking brake applied tightly when parked on hills. This forces the parking prawl inside the transmission to support a large load. The prawl can easily be bent or mis-shapen this way. Then, it simply gets harder and harder to get it out of ‘Park’.

thank you very much for the response, it makes sense