Another drivetrain vibration.

I just had my neighbor drive it. He is the president of a hot rod club. He got it up to 100 mph, laid down 100 ft of rubber, hard braking. Basically, he put it through its paces. He hears a little noise from the back of the car but no vibration. He said he would not be hesitant at all to take it to the track. I need to get back on the freeway to test for any more vibration.
@Locomotion i now remember that when assembling the u-joint it was a bit tight. Maybe I pressed it in too much. I figured that to would loosen up a bit. I need to remove the driveshaft and check its condition. Yes, drive on lift.