Why will my car not go out of park?

What is your question?

My car will start right up and runs fine. The shifter will move between the park, drive, reverse, ect. but it won't actually shift out of park. I tried putting it in neutral and pushing it and it wouldn't move. My tranny fluid is full and a clean red. It's been slipping a little lately but it's been headed that way considering its got 320k miles on it.