Pure speculation on my part here- Slim possibility that the imput shaft and front bearing on the trans might cause this problem. If you slipped the pilot bearing on the tranny and wiggled the shaft to check for play, you've already eliminated this possibility. The usual culprit for this problem is a bad throw-out bearing or a leak from the trans or motor getting oil on the flywheel. The next most likely cause is a bad trans mount or carrier bearing. One piece driveshaft on yours? Probably one of the easiest things to do is have a buddy lay next to your truck where he can see under it while you take off. He may be able to spot the source and save you some headaches. Offer some beer as incentive if he spots the problem, he may climb under it then while you take off!lol. Works for me. | 
