How Do I Fix This

Dog Tracking rear axle. Square your rear axle to the subframe.

Simple cross check from the 1" holes in the front of the subframe in front of the rear axle to the u-bolt threads at the shock plates.

Also put a white chaulk mark center line at the botton of the brake backing plates and cross check measure to there too.

Have seen some pretty big centering holes on the spring perches where the leaf spring center bolts drop into.

Loosen the U-bolts and square it up with a porto-power, or pull it square with a come along, or both . . One on each side to move in desired direction.

Retighten U-bolts.