Shake/bounce at 65mph

[Red Cent]

I have an E350 SD 12 passenger van. 6.0 powerstroke. 97000 miles.Here is my problem. Recently I started to get a bounce round 65mph to 80mph that feels like a bad/unbalanced tire. Michelins LTX. Very good tread. Not worn. I took the van to a very respected tire store (locally owned) and had them balance the tires and rotate them. No change. The problem did not follow the tire. The bounce is felt in the butt, not in your hands. More specifically, right buttock. I took the owner of the store for a ride after and he did not know. I have checked the drive line and I cannot feel or see anything loose, broke, or strange.
Anybody else have this problem. Suggestions?

[Biofuld]

Bad shock? Suspension bushing?

[TANK.]

I get the same thing with my F250 4x4. I did the same thing too and got them balanced. Don't know what's up????

[charlesrf600]

Mine does the same thing as well. I have no Idea what it is maybe bent drive shaft or out of balance worn suspension bushing maybe loose converter

[Red Cent]

Life whizzes by.

I still have the problem. More info follows.

A few years back I had a antisway device installed. Mounted on the right shock brace/support. Double end tie rod type bar ran to brace mounted on frame on the left side. I recently removed it for grins. Changed the "felt" vibration. Now the vibration can be felt beginning at about 30 mph (or before). Very light, very fast vibration similar to u joints. Some sweet spots with barely noticeable vibrations. 45, 60, and 70mph more noticeable. Put new ones in. Same.
Bit the bullet. Replaced BOTH rear axle/wheelbearings. BTW, the races are the axles and the bearings are in the axle housing (E350). Same.
Next I will trade the front left tire with the right rear. Next I will have the driveshaft spun and balanced if necessary. Next I will find a cliff.