Jerking clutch pedal mostly under a load?

Is the pedal pulsing or the truck jumping?
Either way I would guess your flywheel or separator plate is warped. Could also be the actual pads themselves on the clutch disc. I have seen them warp on ag tractors and make it very hard to control things kinda not much and then grabs. Does it do the same thing in reverse if not possibly a motor mount issue look closely at the ones on the sides of the flywheel housing

 

What gear are you using? Sounds like too high a gear for the situation.

 

Mine was like that when I bought the truck. I put in a new clutch. Old clutch still had a lot of friction material left, but the new clutch fixed the problem. I adjusted mine as well, and it didn't help.

Are you saying it's real touchy, like you can't feather it? Basically "all or none"?

 

Good point I guess I assumed that the guy in the seat new about that but come to think of it that’s a pretty common situation

 

Same as mine. Even the slightest incline was almost impossible without stalling the engine, and always makes you look like an idiot.

Not sure what was wrong with my old clutch, because it looked fine visually, but the new clutch fixed it. Refaced the flywheel and did rear main seal at the same time.