Shocks keep stripping?

[71C10Guy]

I've had two pairs of shocks on my 71 c10 and both pairs strip out. More specifically the bolt that holds the bottoms of the shock first gets deformed on the threads, then bends, and eventually breaks through. I have put probably 10 bolts in each rear shock and they always end up breaking. This last time I was driving from Houston to Austin and both shocks came off the rear and started dragging and throwing sparks.

This only happens on the rear and it is always the bottom bolt that strips. Any clue as to why? Could the swing arm be bent or shifted where it is pinching the shock or shifting sideways while the suspension travels?
Thanks,
Mark.