I decided to lower the back of my supercab FX4 truck 2 inches for a better tire fit in the fender wells. To my surprise, the takeoff shudder is now gone. The only explanation that I can come up with is the 2" spacers gave extra leverage and caused axle wrap. The truck looks great and drives great too. The rear is now about 1 1/4" - 1 1/2" higher than the front.

Let me know if it works for anyone else.