I solved my very bad vibration issue after having driveshaft off 2 times. I put new center bearing and holder on, new flex discs, one center bushing, a used driveshaft with a new u-joint installed by me which I tack welded in to keep in place. Total cost

1.center bearing + holder $14
2.flex discs $100
3.u-joint. $14
4.used driveshaft with vibration damper $40
5.center bushing $11
Total cost approx. $180 not counting at least 12 hrs. Of my labor it was a real learning experience like anything you could do it quicker 2nd time around. I think if did it over again I would not worry about the u-joint if it has a notched feeling in it as they are held fairly straight and I do not think that would give you vibration issues. It was a pita to put the u-joint in. Anyway now at 85 mph. my gear shift selector is quiet and I can hear the radio ounce more. It is an important fix as you do not want that shaft ripping lose at 80mph which is what this 85 300 SD likes to cruise at.