The low side could be from the frame rail on that side being bent up a tad. You may try putting a small level on top of the front frame rails. Put it on each side aimed front to back, then compare. I've seen front frame rails bent up on one side from hitting curbs, etc..... Or could one of the torsion bars be weaker than the other? What about switching the torsion bars side to side? Could that be done to rule them out?