When you say you pulled all the steering covers, I assume you mean on the column and also on the double u-joint linkage to the steering box?.... Is something jammed against the steering column linkage anywhere, the draglink etc? Have you bent a steering component offroading and not noticed (very unlikely)? Is your power steering still working normally or is steering effort getting heavier? Of course, you must have checked the fluid level - is there a leak at the pump? Just trying to cover some of the bases here.