I've got a 59' Series II SWB and am having some clutch issues (or so I'm guessing). The problem is a lurching sensation, like when someone who is learning to drive a manual can't figure out how much gas to give it.

When I first start out driving, everything is fine and the transition between gears is smooth (including the double clutching from 1st to 2nd since there are no syncros).

The lurching starts after driving for a bit and really only happens when starting from a dead stop in 1st gear. No matter how hard I try to balance clutch/gas, I almost have to rev the engine too much and let off at a snails pace in order to get the truck moving to the point I can get going without lurching.

I've replaced the master cylinder, slave cylinder and lines, and flushed the entire system multiple times (not a hint of air bubbles). Terrified to hear it's the clutch itself, but with the difference between functioning when it's "cold" vs. lurching when it's warmed up, I'm wondering if that's the case.

What in the damnation am I doing wrong?

Thanks for any pointers