[davew833]

Well, I bled the power steering again by finding some loose gravel and turning the steering wheel from lock to lock about 40 times rapidly-- it was a good arm workout. That seems to have reduced most of the vibration at 60 mph so I'd say at least part of the problem was air in the system. The remaining minor vibration feels like maybe a wheel out of balance which is easy enough to correct. Thanks to Dan for suggesting it's better to do it in loose gravel or dirt.