A quick read of the responses on this topic have confirmed my recent experience with this. Reading it you can find a fair amount of what appears on the surface to be contradictory claims...but it isn't.
The only simple and fully accurate statement that can be made about the topic of truck suspension for a heavy TC is this: it's complicated.
It depends on the make of the truck, whether it is dually or not, what kind of springs and shocks you are starting with, tire type and inflation, personal preferences on sway vs. truck leveling vs. smoothness of ride, etc. etc etc.
My experience with this on three different trucks suggests the following:
1) no standard F-350 or 3500 truck is "ideal" for such a heavy load with out some sort of addition to the suspension
2) Only airbags or only springs to solve the above is not an ideal solution for most. You need a combination of the two with proper adjustment to arrive at something that most people find pleasing.
3) No matter what you do, the final solution is a personal compromise. It won't ever be "perfect". If you get it stiff enough with a combination of springs and bags to take out ALL of the sway, then it will ride rough. You have to find a personal "sweet spot", and perhaps change the airbag pressure depending on how much water you have on board and how windy it is or how winding the road is you're on that day.
4) If "sway" (or body roll) is what's bothering you, having dualies is an important part of the solution. Body roll is a combination of motion in the suspension and a redistribution of weight on tires on the two sides of the vehicle and how the tires respond to that change in weight. The additional width of a dually setup gives it a natural advantage over SRW when it comes to body roll.
