I don't know that the only difference is helper springs. But what really matters is the ratings. The 3500 has 900# more GVWR and 1000# GCWR.
Air bags will not change the ratings. They only give you something else to worry about.
2003 Ram Truck 2500 SLT, Quad Cab, 4x4, Short Bed, Manual 6-Speed, 5. 9L 24V Turbo Diesel High Output engine:
With 3. 73 Axle Ratio You Can Tow 12850 lbs2
Gross Vehicle Weight Rating (GVWR) = 9000 lbs
Payload = 1990 lbs1
Curb Weight = 7012 lbs
Curb Weight Front/Rear = 4269 / 2744 lbs
GAWR Front/Rear = 5200 / 6000 lbs
Gross Combination Weight Rating (GCWR) = 20000 lbs
2003 Ram Truck 3500 SLT, Quad Cab, 4x4, Short Bed, Manual 6-Speed, 5. 9L 24V Turbo Diesel High Output engine:
With 3. 73 Axle Ratio You Can Tow 13750 lbs2
Gross Vehicle Weight Rating (GVWR) = 9900 lbs
Payload = 2820 lbs1
Curb Weight = 7080 lbs
Curb Weight Front/Rear = 4277 / 2804 lbs
GAWR Front/Rear = 5200 / 6150 lbs
Gross Combination Weight Rating (GCWR) = 21000 lbs