I had a 2005 Itasca Horizon that had a steering wheel shimmy from the time it was new until 37,000 miles were driven. During that time (four years), I took it to the local Freightliner facility twice and three different truck tire shops. They balanced the wheels, installed Tru-balance wheel centering, installed Equal in the tires, etc. No one could solve the problem so I continued driving with the annoying shimmy, even after installing new Michelin tires.
Later, I called Tolleson Freightliner, west of Phoenix. Kirk Ault, the Service Manager, assured me they could eliminate the shimmy. When we passed through Arizona, I took my coach to them. They measured the radial runout and found it out of spec. They rotated the tires on the rims until the runout was within spec. This solved the problem. When I drove away the steering wheel was perfectly smooth at all speeds for the first time ever.
Note: On several of the many failed attempts to solve the problem, I asked the service person to check the radial runout. Each time they said they did and it was in spec. They either did not know how to properly check the radial runout or they never actually checked it. As I recall, it takes a special tool that some tire shops do not have.
Good luck.
