2002 F150 5.4L RWD.

I recently replaced my lower ball joints, upper control arms and ball joints, wheel bearings rotors and pads. I had a local Firestone with a good reputation perform an alignment after I finished the rebuild. The camber and toe were out, but adjusted to well within spec. The caster before and after (there is no adjustment on this front end) are +7.1 passenger side and -7.4 driver's side. WTF? First, +7.1 is just barely within spec, according to Firestone. But, +7.1 and -7.4? To me that suggests that something is bent, but, I'm a novice and I suppose there could be several reasons why the caster could be that far out.

Update: I'm going to check the bushings on the lower control arm. Thinking through it...other than something being bent...the lower control arm bushings being severely worn are the only thing I can think of that might cause the steering knuckle to rotate.

Truck seems to track and steer fine. No pull. Re-centers. No apparent problem in the steering.

So, is it a problem that the caster is opposite polarity side to side? I know that theoretically, there should be some lift through steering on one side, and dip on the other, but slight. Enough to matter? Any way of tracking down what is causing the difference in caster side to side? (Paranoid parenthetical...is it possible that I installed the control arms on the wrong sides? But, even that shouldn't cause an opposite polarity in the caster, should it?)

And, on a slightly different matter...I asked the technician if their numbers are referenced to spec, or to "zero." He said they are referenced to zero, which made me wonder if the machine they use takes into account Ford's factory specification for camber. Anyone have any insight into that?

-Kokomodo