My '51 1/2 ton did that until I replaced the springs. New springs raised the front about 2.5 inches which put the steering geometry where it should be. When the front sags because of tired springs, the steering box is not centered when you are going down the road because the drag link is not at the proper angle,
My steering wheel rotated about 180 degrees from where it would sit in the straight ahead position after I put the new springs on. That shows you how much it was off.
Anyway You might check out your springs and see if they are looking flat. Fairly easy job to replace and not too expensive either. Check out SDtrucksprings.com.
1947-1955 truck springs Replacing these springs was the best thing I ever did for drivability and steering.
Kurt