RADROG wrote:
My girlfriend was following me one day in her Jeep and I'm in my 2002 Chevy 2500HD and told me it was "Crab Walking". She was a competitive "Rock-Crawler" so I figured I better listen to her and check it out.
Turns out the rear U-Bolts loosened and sheared the drivers-side leaf spring centering bolt causing the axle to shift position on the driver side leaf pack.
New centering bolt and a re-torque on the U-bolts and it was aligned and good as new.
I believe this is the correct answer, the center bolt on one of the rear springs is probably broken and the spring has slipped one way or the other, U bolts allowed this movement when the center bolt broke. The center bolt is put through the spring leaves and then sits in a hole in the axle saddle with the U bolts holding the spring unit in place. Give it a look, might be your problem