1990 Ford E-Series Van king pins

The kingpins would be the last thing I'd suspect & you'd need the service manual + special tools to do that job right - it's not a Saturday afternoon in the driveway project.

1st thing I'd check would be the front tire wear & front end alignment - especially if you carry varying loads. The problem could be elsewhere & the steering box would be the next place to look, but since the front end camber changes from no load, to load in the front, load in the back, etc, the van can act pretty strange sometimes when there's really nothing wrong mechanically.

Somebody who really knows Fodr van/truck front ends can tell a LOT just by looking @ the front tire wear & checking the tire pressure - also knowing what (if anything) you carry in the van.