It sounds like you're still experiencing "rut tracking" where the front tire follows the depressions in the pavement.
My experience: 38 ft air bag chassis with track bars front and rear. Pretty good handling after I got the slop out of the steering gear. Installed a Steer Safe (the device with the springs) and it absolutely eliminated the rut tracking.
My suggestions:
1. Be sure you don't have more air pressure in front tires than required.
2. Although the safety plus steering stabilizer says it helps with rut tracking, it sounds like it is not eliminating the rut tracking for your motorhome. Of course, it's fairly expensive to switch steering stabilizers. Maybe you could check the shock absorber portion to be sure it does not have weakness or wear.
I have no experience with spacers for the duals...sorry.
I think you said the rig is 33ft. Is the wheelbase to length ratio greater than 53%? If no, this could be contributing to the problem.
Let us know what you find.
Fred