Vibration in drivetrain

I had the same problem. I put the car up on jack stands and ran it with the wheels off, without brake drums on, without axles, swapped 3rd members, changed the trans bushing, every pinion angle from -5 to +4. Had a new driveshaft built and it got way better but its still there. I bought a inexpensive shaft from Dr Diff. If I had to do it again I would buy a shaft from someone with a high speed balancer.