It's really pretty simple- - - - -just remove the rear shaft by unbolting it from the rear end, slide the slip yoke apart and reassemble it with the yokes aligned, or 90 degrees apart. Don't assemble the shaft in such a way that the crosses are misaligned by one or more teeth. The vibration comes from the driveshaft tube trying to twist as it turns, instead of the yokes flexing as the shaft rotates. Some of the smaller shafts have a keyed spline so they can't be assenbled wrong, but the larger ones have to be indexed properly as they're assembled.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!