Vibration in steering wheel

I had a similar problem. I had a slight vibration. Lots of good thoughts on the boards. Ford even tried to figure it out. Checked tire balance. Checked the balance of the drive shaft. Then one day I was talking to a guy who said " sounds like your missing a plug". Sure enough, my # 8 plug was bad.
Does the vibration happen when you are going up a slight hill? When your motor is pulling harder? My steering wheel didn't pull, and the vibration wasn't visibly noticeable. But you could feel it.
Mine is a Ford F53 05