It drives fine in first and second. It will shift to third but when you let off the gas it will halfway go into second and stay there. I give it gas and it acts like it's in neutral and it will eventually go back into third until it's given little or no throttle, then back down. Any ideas?

 

How many miles on the old girl?
You could service the trans... R&R the valve body and clean it. also adjust the bands.
But if you drop the pan and if it's full of Lining in the bottom? Then it will need a over haul.

 

Ya Bob!