I also agree it is more than likely tire related.
But if you also do want to add a steering stabilizer, I would suggest the Henderson Trim Kit system vs any other. I would stay away from the Trucenter system from BlueOx, see...
http://www.irv2.com/forums/f59/trucente ... 79623.html
Here is the info on the Henderson Trim Kit...
http://www.hendersonslineup.com/product ... assis.html
Note..The BlueOx and the Henderson system are not just stabilizers, but also allow you to TRIM the center line of the coach while driving. Example, a crown in the road that makes you keep holding the wheel to the left or the coach would drift right. With the trim you can press a button and "trim" that out so you no longer have to keep holding the wheel left all the time. (It trims out the tie rod.)
So the above is differnt then just the Steer Safe. A better way than the Steer Safe if you do not want the trim, is to used a Safe-T-Plus on the Tour Master
http://www.safe-t-plus.com/ (You need the Blue Colored one.) The Henderson Trim kit also uses this part as part of the system. So you could just start with this and have the trim kit added later if you want. (The trim kit just allows you to adjust this.)
Such items help with wind sheer and also when semi trucks pass. They help a lot with bumps and pot holes. But where they really shine is if you have a front tire blow out. It will help to keep the coach from jerking left or right.
I would not drive without one. I also will always have a way to adjust my trim.
Sorry for the long post.