Originally Posted by Remeniz
When you say 'on the lift' I assume you mean the wheels are off the ground?
The tranny will go through all the gears on a lift. If it won't on the ground then you need to look at the internal oil pressure. If the pressure is low then you wont get 3rd or 2nd sometimes. Also if you can adjust the brake bands then make sure they're adjusted up to the correct torque. Check the govener near the output shaft too.
Automatic transmissions rely a lot on the pressure of the tranny fluid. Maybe you need to replace the pump? Maybe you have some bad clutch packs on 3rd gear? Maybe something is in the wrong place on the valve body, they have a complicated system of veins, ball bearings and springs that if not installed correctly will not function properly. If it's been rebuilt before something like that may have happened.
You just really never know until you tear into it. Auto's are complicated pieces thats for sure.