its a high pitched harmonic vibration; actually deafens you at a certain road speed inside the cab. its like some sort of harmonic or resonance. it could be engine, clutch or driveline as the frequency is so high and i bet it is something involving that torque tube/ujoing setup.
i'll report back when i get ready to tear into the transmission/tube for help as i know nothing about these enclosed bearings and ujoints.

thanks for all your help
tony

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