I have a 2006 f 350 DRW admittedly a different truck, I have a 2002 Lance 1130 which is heavy also.
When I bought the truck it had Firestone air bags. Since that time I have added one fix at a time, upper helper spring spacers (similar to "Towpro") then added lower wedges, similar in purpose to the "Torklift" lower helper spring spacer. These two items helped but just didn't feel right. My truck came with sway bars front and rear, I replaced those with Helwig bars (much thicker) made night and day difference. I think the sway bars were the biggest bang for the buck, helping with sway and overall handling, For me they were the single best thing I did to improve handing and side to side sway. The air bags for me were never right, when I applied air (and it didn't matter the pressure, I tried all different pressures) it just did not seem to help. I took them off and installed Timbrens, I haven't taken a trip with the Timbrens yet but just minor trips to fuel up or into town seem to be a big improvement. I will see when I get loaded up and actually take a trip. I have a feeling the Timbrens will be an improvement.
I know our trucks are different. and there are many years between them, but this is what helped the handling of my truck. Of all the reading on this and other forums I have found that everyone is different and every ones situation is different. Basically every one seems to try Air bags, they just didnt really work out the way I had hoped and I finally got rid of them.