Hey guys i just finished the rebuild on my th-350 and i let it run for a while to get all the fluid flowing through the trans and i know it was pumping i checked the cooling lines and it was pumping, but when the trans was finally full i got in the car and ran through the gears then checked the fluid after that and it was still full so i got back in and held in reverse at mid rpms and it after a few seconds it slowly slipped into gear and moved back a little bit then stopped moving, i tried that in all the other gears and they had no movement so could you guys give me some help to figure out what it would be. Any suggestions are appreciated thanks

when you checked the fluid was it warm/in nuetral? Sounds like the symptom of not enough fluid. Other than that, someone else might want to chime in