did you have the car on the rear suspension when it was lifted? or was the rear hanging free in the air?

I had a similar issue, vibrations at 60-65 in my big block Dakota. with the weight off the driveline, and no load on the engine, there was very little vibration, but it would rattle your teeth out when you were going down the road.



my problem turned out to be an out of balance driveshaft, but my point is that don't be surprised if the vibration goes away when you are free-spinning the wheels with no load and no weight on them.

got a chassis dyno nearby? that will let you run it up to speed, under load, and be able to see everything, without having to jack it all up in the air.