was it a stock replacement clutch disc and pressure plate?
Yes.
But it sounds more like your describing chatter(or what could be described as grabbing) as you slip the clutch to get the truck moving. Does that describe your problem better?
Yes, this is the issue. I used to call it "chatter" as well but to some folks this implies some sort of noise, so I did not was not sure what to call it. Also I generally equate clutch chatter with a worn clutch that has become glazed, which is not the case here. Anyway this is probably just my bias creeping in, I agree it's clutch chatter.