I finally narrowed down my vibration problem awhile back.  It was the angle of the front DS pinion u-joint.  I purchased a front DS from Tom Woods, it is their mulitple double cardan joint shaft.

First, the workmanship is top notch, and shipping was free.  It is much heavier duty than a stock XJ front DS.  It came with their "Gold Seal" u-joints  These u-joints are warrantied against breakage.  If they do break, and damage the DS, they will repair/replace the DS at no cost. 

It required a different flange/yoke on the pinion, and I had the dealer who rebuilt the diff install it today.  Other than that it was as simple as bolting it up to the new flange, and TC yoke.  Actually the new flange is the same yoke as is on the TC output shaft.

The DS eliminated my vibration problem.  I will say there is a VERY slight "buzz" feeling at 58-60 mph.  I was told by them that can be expected since the cardan joint at the pinion is heavier than the single u-joint it replaces.  It is nothing that I will worry about.  It is very slight, and isn't enough to cause any problems.  All in all, I am very happy with the DS, and recommend Tom Woods to anyone who experiences the problems I've had with the LP Dana 30 axle, or any other DS problems.

I will post up pic's as soon as I can get the time to take some.