Transmission problems

I can't say for sure but get someone to check inside the transmission for a plastic piece with teeth on it. Some of the teeth may be missing causing your dilemma. That happened to me once although it wasn't a Grand Am (it was a Ford Taurus) it saved me like $1500. I had 4 shops tell me to replace transmission thank God for a friend of my ex husband who told him about the plastic piece, $20 and an hour or so and it ran like a top.. hope this helps!