Power Steering Woes

I acquired a 2009 DCLB TRD Sport PreRunner that had a dash fire back in 2009. It had been sitting for several years when I got it. After new dash wiring, Ecu, instrument cluster, and body computer/ fuse box and a visit to the dealer to program the keys, it now runs and drives. The only remaining issue is the power steering. Fluid looks good, and driving above 20 mph everything seems fine but at low speeds there is no assist. I loosened one of the lines on the rack and had a helper turn the steering wheel, and there was a squirt of ps fluid, so it appears the pump is producing pressure. I have read the posts about the u-joint that corrodes and binds up but mine looks new, and I have already sprayed PBBlaster on it a few times. If I jack the front wheels off the ground with the key turned to release the steering wheel lock without the engine running, I can grab either front tire and turn it lock to lock easily, so I don't think anything is binding. The PO installed 285 70 17 tires on ProComp wheels with 6 et. Would that tire and wheel setup be the problem?