It seems that air bags are almost a must. I've installed several sets. My brothers Ecodiesel sagged with a canopy and a storage drawer setup in the bed with some tools. Seem to tow well up to 8000 lbs or so, the most hes done.
I put 2” McGaughy’s drop springs on mine with Super-Ride air bags in the middle to reverse level my ‘14 1500 ED. It was a super easy install and I really liked the way it handled and towed before, but much more so after that. I rented a all steel car trailer and John Deere hydrostatic tractor with a loader and bush-hog on it several times. Don’t know exactly how much it weighed but the truck handled it like a champ. I was really pleased.