I have a Ford F550 with Link Manufacturing Ultra Ride air suspension system. Water in the system is the big issue so if yo are spending the money buy the air drier up front.
The ride is great and self adjusting. This is not the Firestone air bag system to help level the truck while still using the leaf springs. The Ultra Ride replaces the springs. Kelderman has a nice system too.
The systems are expensive but if you are doing the miles or the roads are not great then it is a terrific solution to a bumpy ride.
2004 Ford F550 6l Lariat SuperCrew, Fontaine Bed,
Link Systems Air Ride
2011 Sterling 32RL with Michelin XPS tires