Trying to track down bad vibration

[Jim S]

I still have a bad vibration from about 35mph on up.  I can rev the engine in neutral up to 3,000 rpm and it's smooth as silk. But driving in gear the car vibrates.  I put it on jacks and removed the rear tires and it still vibrates running in drive, so it's not tire imbalance.  I also replaced the ujoints and the motor mounts and rear transmission mount.  I'm baffled!