4 speed problem

Bob, had this exact issue. I changed the pinion angle using 4 degree shims and changed the springs. Talking to guys who have raced 4 speeds for years, they all say that what you are describing is rear suspension related. To see if this is the case, you could put 3 to 4 clamps on the front section of your springs. If it helps, you know the rear end was rotating up to fast causing the extreme vibration. I made my clamps from steel purchased at home depot.