I'd start by checking the linkage geometry;if everything is like it should be,try taking it back to the mechanic and asking him to replace the steering box. BTW-he had no business releasing the truck to you with the steering like that;if you wrecked it on the way home,you could own him,if you lived. In our shop we would've (and several times did) worked on it until we were sure it was right and safe.
Speed
