I'd start by putting a jack stand under both sides of the axle and seeing how hard it is with the tires off of the ground.
I never heard of a power steering pump failing without making some noise.. Or freezing up entirely.
Also I'm thinking waaay to much caster would cause hard steering, and low air would make it worse.
Big JIm <img src="/forums/images/graemlins/pfft.gif" alt="" />

professional bovine relocation specialist