check for a kink in the powersteering lines. I had my pump off and when I put it back on the truck was hard to steer. Apparently when I took it off I ended up kinking the metal line that runs to the rubber one.
I have seen where the king pins were partially siezed in the IBeams on one side only and it was very hard to steer or turn at low speed Jack up the truck and see if it is tough to turn with no weight on the front end. If your truck has been pulled out of a ditch or whatever someone may have hooked part of the steering parts.