Your 2500 coils may not have enough spring rate for that AF811 - The 3500 leafs have a 500 lb higher rating. The air bags may help sag, but they may induce more sway. I know there are are aftermarket heavier coils available for the rear, but I don't know if going with some Timbrens, Sumo springs or RideRight taller compressible bump stops would be better than bags.
My 2012 AF811 was about 4000 lbs when loaded for a trip and over 3000 lbs dry - I don't think they are making them any lighter now, but I did have almost all of the heaviest options.