If it was a problem with the flywheel needing to be replaced from being worn down, then the problem would not be that it's slipping, but that it wouldn't fully dis-engage. And yes, everything else was replaced. Brand new PP, Clutch, throwout bearing, and the master is out of my old XJ, and that was only a few months old when the truck was junked. I think it's simply that something is not allowing the slave to go back all the way. I'll try shimming it when I get the chance.
The difference may be in the aluminum spacer that goes between the Slave and the flywheel?