Ok, my 99 f350 PSD...It has a strange steering wander binding issue. I have been reading here and other sites on the internet, and have yet to find anyone with the same problem, similar but not the same. It started about 3 months ago I noticed the truck was hard to keep straight, I had to constantly adjust the wheel to keep the truck in the lane. Pulled it into the garage, checked all the steering and suspension components. The tie rod at the Pitman arm had some movement, so I replaced that first, that only made the stiffness/wander worse. I knew the right side lower BJ was loose, so I replaced all 4 ball joints, U-joints at the wheels and hub bearings and had it aligned. Still the same. I tried adjusting steering box, no difference, so I replaced the box, pump and line, flushed the cooler and refilled it with synthetic P/S fluid. It steers alittle easier, but still binds in the straight ahead position. It feels stiff it the straight ahead position, but if I move the wheel 2" to the left or right it feels good, also if I go one full turn the wheel doesnt bind so I'm thinking its not in the column (no movement in the wheel or steering shaft.) I tried removing the steering dampner, no change. I removed the steering arm from the gear box, and the binding is gone, that tells me its not in the box or column. When I move the wheels by hand there is no binding, but when everything is connected the wheel is stiff going straight, the only thing left are the outer tierods, and draglink..they were new last spring. But even new parts go bad!!! I also tried tire pressure adjustments, 35-80 psi in 5psi steps, rotated tires front to back. Im out of ideas... I tow a 30ft trailer that is 10,000lbs loaded, and the truck is squirelly by itself, i dont even want to tow with it, if you have any ideas, I'll try it, thanks

 

Almost a sounds as if the steering box has some problems is either the valving, or work gear. It is not uncommon for the gears to wear in one area since this is where they are used most often.
Rust or corrosion due to water or a lack of fluid maintenance can also contribute to this problem.
Once everything has been removed, you should be able to isolate the problem, but it appears that you have narrowed it down to the box itself.

 

I replaced the box already, and with the steering linkage disconected, there is no bind.