Take your coach to a well equipped shop that has the equipment to check the thrust angle on your rig. I am sure that you will find that the rear end is not in perfect alignment with the center of the coach. If the rear axle is not aligned properly, the front end alignment is close to useless because the rear axle is always trying to push the front end sideways.
Any shop that has the right equipment can do this. The other shops, that do not have the equipment, will tell you that the rear axle is not adjustable(they are wrong) and that all you need is a front end alignment.
Thrust angle adjustment
