kenc, i have new radials and wheels on the rear and i'm think they balanced them corrrectly. the vibration seems to be more intense at cruise and trailing and eases off under acceleration. it is also present with the trans in neutral and the clutch out (foot off the pedal). it seems to clear up the instant i hit the brakes although that could be because i'm bringing the speed under 40 and that don't take much cause i don't drive more than 50. i'm pretty sure i'm feeling it in my feet and also in the steering wheel and gear shift lever. i dont' feel it in the driveway revving the engine in neutral, not moving.
what is it?

Overland Blue, 1953 GMC 1/2T, 100-22, 228/1bbl, 4sp/4.10 6v, shortbed/fender side/5-window.