Coils sprung Superduties need more damping up front than the leaf spring models. The smoother you want, just go further and further up the Carli $$$ list. But the further up you go, the more you compromise towing. Towing with a 4" lift and 38" tires, stinks.
IME, it's the lack of proper damping that makes the ride harsh. Usually firm shocks smooth out the ride a bit. Firm, but controlled. My factory shocks were extremely harsh in the front at 100,000 miles.