Back when I worked for a Freightliner dealer in the truck shop we had many complaints from Freightliner Custom Chassis Motorcoach owners (Class 7) about wandering steering.
99% of the time there were no mechanical defects, just drivers that were unaccustomed to driving a vehicle with the high GVW. What I found worked best for advice to the drivers, (and for myself) is to drive with both hands on the wheel (10,2 or 9,3) and leave your elbows resting on the armrests...it helps to fight the urge to "oversteer" the wheel whenever the front wheels follow grooves or the coach sways a little.
This works for me on my heavy 3171DS towing a heavy car.
As well, when driving tour coaches or tractors or class 7 coaches or fire engines they all behave the same as mentioned above...to me it is nature of the high GVW vehicles.