The W series Workhorse chassis has massive steel to steel anti-sway bars installed from the factory. That is the 3"x3" square box by both the front and rear axles. There are no bushings to wear out so forget about that being the problem. They do not look like the standard anti-sway bar but they are much better. Of course some of the people that SELL traditional anti-sway bars are more than willing to take your money.
I added air bags to the rear of my W chassis and by adjusting the air pressure, I can travel in strong crosswinds out in the Great Plains.
I know that your chassis came with Bilstein shocks, that have a lifetime warranty, but they still could be bad and not dampening the rocking motion. I replaced my Bilstein shocks with Koni FSD shocks.
