I assume that the shuddering occurs while you're driving down the road? If so, what happens if you shift the tranny into Neutral while it's shuddering? Or does it also shudder if it's been sitting still idling for 10 minutes?

1977 CJ-7, fiberglass body, AMC 360 w/ headers, DUI ignition, Edelbrock intake and Holley 4150 carb, TF999, Dana 300, 4.56 gears lockers, York air comp, 4" susp lift, 2" body lift, BFG 35" M-T tires, Megashifter, AGR pump & box, REP8000 winch.