Steering shaft issue?

[Fake Name]

My '70 F250 has been developing a steering problem. It likes to "hunt" down the freeway- minor L to R movement, it's hard to describe. Like the truck is in a crosswind. I've had the entire front end checked out, including different tires.

The kingpins are fresh, as are all the other bushings, the alignment is set front and rear. The front shocks and springs are new, as is the steering box and rag joint.

I read in the LMC truck catalog that my problem could be caused by a bad Steering Shaft Assembly. Of course, they describe the issue on the page where they are *selling* chrome moly, needle-bearinged deluxe steering shaft assemblies for $329.

Anyone experienced this issue?

thanks.

fn