'68 Chevy pulsation while driving.

[luke1968c10]

I have a 1968 Chevy C10 250 six cylinder 3 speed on the column. It has been in my family from 1973 and the odometer has returned to 00000.0 four times so now it has 591000 miles on it(engine was rebuilt at 567000 but everything else is original.) It is mostly stock but I recently replaced the points with an HEI distributor. It has a pulsation that coincides with the speed of the wheels turning. It occurs in all gears and goes away when I press the clutch or go to neutral. There is no noise associated with it. I have replaced all four brakes also replaced front wheel bearings. I topped off the oil in the transmission and the rear end. I can usually figure out any problems with this truck but this one has got me. Thank you in advance.