I'd also change out your U-joints, as these are a common cause of vibration. Sounds kinda silly, but also check your U-bolts on the springs. I had an old blazer, that they came loose on, and caused a wierd vibration that i couldn't find until I'd tore the entire driveline appart. Can cause the axle to wrap some, which will change your pinion angle and can cause early death to other parts.
Good luck
Erik
