After being in park, I back up and then the car will not shift into drive to go forward

This problem does not matter if I have been on a hill parked, or on a flat surface, it will just every once in awhile not shift into gear to go forward, after I have backed up. It feels like there is nothing that will catch when I am shifting. I can shift it a few times and it will then act normal, or I might shift it for an hour before it will catch again.

I have tried turning the car on and off, step on the brake, not step on the brake, turn the wheel, not turn the wheel, and cussed a lot. Nothing seems to work. It just goes back to normal when it is good and ready.