I just switched from an 07 3500 ram dually, to an 08 4500 and to my surprise, the ride was better in the 4500, even empty, plus it's 4 wheel drive. I have no idea why, it just is.
It also turn in a smaller radius. I'm about to mount the AF1150 to if for the first time, and I'll let you know how it does, but with a GVWR of 16400, it should be fine.
When I brought the truck home, it was a 200 mile plus trip, and hand calculated I averaged about 18mpg at 65mph.
I'm about to do the EGR DPF delete, so I'll keep you posted on the mileage.
The real trick is to keep it under 65. According to the Cummins research paper, 65 point where wind resistance begins to use the majority of the energy, and I believe them.