Holy crap!
You've got a serious binding problem.
What is the angle of the pinion? What is the angle of the trans tailshaft? Are you sure the rear end is centered in the car correctly, as is the engine and trans?
I'd have that rear end double checked too. Check the mountings and the internals.
On first look I'm wondering if the rear is going completely negative on pinion angle (down below level) under power.
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Freedom is never more than one generation away from extinction. We didn't pass it to our children in the bloodstream. It must be fought for, protected, and handed on for them to do the same.
-RONALD REAGAN
462 cid/ 6x-4/ TH400/ 3.36:1/ 28x10.5/ 3880#/ 12.35 @ 109.36/ 1.69 60 ft/ 4 wheel disc brakes/ 15 mpg