I own a 2003 Bigfoot Industries Class C motor home Model 30MH27DSL built on a Ford E450 chassis with 7.3 L Powerstroke Diesel. It only has 24k miles on it. It had a vibration mostly felt in the driver seat and most predominant above 60 MPH.
After getting driveshaft hanger bearing replaced and all tires balanced (twice), my vibration problem was isolated to a bent driveshaft. Driveshaft was straightened and rebalanced. This fixed the vibration problem. Hope this helps any others out there experiencing similar problems.