steering problems

[gafiredog]

I need some help with this, My 1987 crewcab dually was used before I got it to haul cars on a hotshot 5th wheel trailer. the steering was shot, along with the brakes. my problem is, every time I hit the brakes it jerks left or right every time, especially if i hit the brakes hard. I have replaced everything in the frontend except the ball joints, and the steering box itself. I have installed new brake pads, and calipers. and put on new tires. I even installed a steering damper. it still does it. any ideas on the problem ?