Vibration between 60-65 mph

[HandyDan]

I just got back from the lake.  The old Holiday Rambler ran just great the entire 300 mile round trip with the exception of a pesky vibration in the 60-65mph range.  It isn't bad and is a lot better since I put new shocks all around, but it is still annoying.  I have replaced the center driveline bearing, had the tires rebalanced, and, of course, new shocks.  It seems to be on the passenger rear side.  I have a tag axle so there are three tires there.  I would think they would cancel each other out if they were out of balance.  Any ideas?  I'm going to switch some tires around and see if the vibration migrates with one of the tires.  Thanks for any help.
Dan

[LJ-TJ]

I've had a similar problem in the pass. I had steel belted radials on at the time and while the tires balanced out ok it was the steel belt that was separating.

[Oz]

What happened when you got out of the pass?