stang831

Just finished swapping a ls1 and 4l60e into a foxbody. Went to drive it for the first time yesterday and the transmission was slipping in all gears. It was a little low on fluid, so I topped it off and went to drive it today. It started out slipping and barely moving but after running it for a 5-10 min it was getting better. Now 1st gear pulls hard at wot but 2nd pulls until about 2k and then just shoots to redline. The motor/trans came out of a wrecked fbody that had been sitting for no telling how long, is it possible it just needs to be ran and each gear will slowly get better like 1st and reverse did? Or should I start looking at a rebuilt unit?