I've check the lug nuts, axle nut, hub bolts, caliper bolts and slider bolts; they're all tight.

I've checked the control arm bushings, sway bar end links, track bar bushings and boot. The boot on the track bar is shot; gonna replace with Moog. All else are fine.

Checked pitman arm, inner/outer tie rods. All Fine

I've got a friend coming over tomorrow. we're gonna hit a parking lot and see what he hears.

 

Did you figure out anything new? Besides hearing a clunk can you feel it as well? Floor or Steering wheel?
Try this, while driving 20mph push the steering wheel up and away from you firmly, then slam the brakes to make the truck nose dive. Is the clunk sound and feel more noticeable? If so I'd look at the column for the problem.