Shutter on clutch release.

[Mark B]

I have a 1970 C10 that shutters badly when I back up an incline. It shutters when the clutch grabs and the truck starts to move. I had the clutch replaced and broken motor mounts replaced, but problem is still there. The warped flywheel was also trued up. The truck is a shortened LWB, leaf spring, 3 on the tree. The transmission has no rear mount to the frame, nor does the driveshaft. The truck didn't always shutter this way, so I don't know what the problem may be.

Does anyone have any ideas for me?

thanks