You vibration is not very likely to be coming from the 4 link setting IMO, given your stated pinion angle at least. Nothing else back there can cause that. If it is rubbing the tubs thats likely tire growth thing. The 4 link is not causing it to rub unless there is something VERY VERY wrong with the set up or shocks settings. I for the vibration I would be looking for a new driveshaft myself.

"I am not ashamed to confess I am ignorant of what I do not know."

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