[FredG]

I love a good challenge. You say the frame to ground measurements are the same on both sides. Are the measurements taken right in front of the rear wheels. I would pull both rear wheels, put jack stands under the axle and start inspecting the frame to body and frame to axle connections. With that big a gap, something should jump out at you as being out of whack. Did this problem appear after the shocks were changed? If so, take the rear ones off and see what happens.

Fred