[rlith]

I doubt if it's your rear axel bearings. I would more suspect a bad/bent drive shaft or a bent axel shaft with the symptoms you describe...

Usually with a speed cauised virbration like that I would be looking at the axel shaft. Granted, a bent axel shaft could cause one of the axel bearings to go bad, but it's unlikely.

When they replaced the u-joints, did they replace both or just one?

Also for giggles, I would have the motor mounts checked.