I have the same problem with my 56 half-ton. I went through everything, and determined that all the play was in the steering box. I adjusted the steering gear according to the manual and got it so it was really nice to drive. But after driving the truck for a few weeks, the freeplay returned. My kingpins, bearings, and tie rod ends are OK. I'll be rebuilding the box at some point. A rebuild kit from Classic Chevy Parts is currently going for $64.
