[Cobra20646]

Gary,
If I'm understanding your post, the vibrations are severe AFTER the engine has reached 5 grand or so. After shifting to higher gear (3rd), the vibrations are minimal until higher the revs are met agian right?
If that's the case, I'd rule out anything south of the transmission and look at that new clutch. Did you have the flywheel re-serfaced? Clutch plate located DEAD center? Good pilot bearing? All bolts loc-tited and torqued? Sounds like it's engine RPM related to me.
I've had U joints vibrate under acceleration, but they got worse as shaft speed went up and were independent of engine RPM.
- Jim -