I have had 2 posts on this subject. can't find them so will put this in at this point for information. Shaft vibration on a smooth road and with good tires can be felt while driving. The amount of vibration depends on how much the shaft is out of round. Ford has set up a maximum of 35 thousenths, mine was 28 so even though I feel it they say the shaft is in tolerance and buying a new shaft will not necessarly improve the situation. This amount of out of roundess should not have any affect on the life of the output bushing of the tranny I am told.