When taking the off ramp of a freeway at 55 mph and pushing the clutch pedal to the floor and foot off the gas pedal I can feel a vibration from under the floor board. Does that sound like u joints, driveshaft? I did replace my clutch last year and did not balance the pressure plate and flywheel together. I was told I did not have to since the pressure plate was neutral balance. I did resurface the flywheel.

I chased a vibration like that for a year, turned out the tyres were not balanced correctly.

It did not vibrate before I replaced my clutch last year.

So, are you saying that it does not vibrate while slowing UNTIL you disengage clutch disc?

Yes. It does not vibrate until I push the clutch pedal to the floor.

What type of clutch ? Pop the cover off and look at the throwout bearing and see if it is off center of the clutch fingers ?

Are you very certain that the u-joints are secured and centered? If so, make sure the 4 trans bolts are tight in bellhousing.

It's a Mcleod Borg and Beck clutch. The u joints are centered and all bolts are tightened.

When you pulled the drive shaft did you mark it's phase with respect to the rear diff? How bad is the vibration...teeth shaking or just noticeable?

No I did not mark its place and it is not teeth shattering but very noticeable.