Please help me diagnose a vibration in my Dart.

Well, I had new solid U-joints and a new transmission yoke installed, and had the driveshaft balanced.
I think the vibration is gone. I still felt a little in the steering wheel but it didn't pulsate and drone like before.
I let my 21 year old son drive it while I sat in the passenger seat. It was really smooth in that seat. Then I drove it and noticed that little bit of vibration in the steering wheel.
Having the front wheels and tires balanced is next.