1996 oldsmobile 88 transmisson is doing very weird things

OK, here is the problem. I own a '96 oldsmobile 88. The transmisson wont go into gear. (any gear) The shifter moves back and forth just like normal and the car changes idle tone/speed just like its going into gear but the car wont move. If you give it a little gas you can tell the engine is under some strain, like its in gear. OK now here is where it gets weird. After you put in and out of gear like 100 times, it will just work great, like its supposed to. And it will drive in forward in all gears and you can drive in reverse also. but if you put it back in park it starts the whole thing all over again. I can't figure it out, please help
the car has 130,000 miles