Just to close the loop here. I found out that my driveshaft that had been "custom balanced" was not really balanced at all. The new shop check it and it bounced their rig pretty hard. They found that the rear yoke was .015" offset and the front U-joint was undercut allowing it it favor one side. They got it all happy again and I tested it this past weekend and what a difference. It runs up to 90mph and really smooth!!!!! Now if I can figure out why the glove box pops open at speed???

Jim
68 Hemi Road Runner