Mystery vibration at 25 mph can't be diagnosed. It's not the front end!
One quick-n-dirty diagnostic technique for a B&T U-joint is to undo the nuts holding it to the transmission output flange, install two good quality flat washers on each of the four flange studs, and reinstall the B&T over the washers. If the vibration changes at all, that is a further indication that the B&T is worn out. It's not 100% sure-fire, though, depending on the nature/pattern of wear.
