Driveline Vibration

[tdangle]

C20 stock ride height, 4.10 31.65" high tires 7004r trans. I have a vibration that comes on at about 55 and blurs the rear view mirror. At about 70 the speed of the vibration is higher and not shaking the mirror. Also a droning is noticed.

2 piece drive shaft rebuilt and balanced by a local shop. Did not shop vibration.

Installed the 7004r trans had driveshaft shortened and balanced no change

New Tires, balanced and then rebalanced with a road force machine no help

installed pinion shims to adjust angle as recommended by shop. slightly better.

New brake drums no change

Today, I put the axle on jack stands and ran to 55 still there. I removed wheels and drums, no change. reclocked the 2 piece drive shaft a couple of times no change. Then I left the rear part of the drive shaft off and smooth as can be. It is either in the rear driveshaft portion or the rear end. (dana 60 full floater)

any ideas?