Just FYI....spring assist ( which I chose ) or airbags do not "change" the official rating. HOWEVER, On Dodge HD trucks, the mod equals bringing your vehicle up to single wheel, Dodge 3500. Obviously a dually is better and the best option.
With that 6.7 Cummins TD, you can pull the world! 😳 My 2008 has been 35000 towing miles and we love the truck. We generally only use it for a TV. Thus, the "spring assist" vs air bags. Without the RV, rear seat is bumpy. But again, we rarely use it.
We now have a 2015 CC Silverback 36 ft and NO SQUAT. This thing is GREAT!
I would really consider and recommend a dually for those greater pin weights. At our age, over 70, last fiver for us. We are leaving soon for east coast 3000 mile trip.
Good luck and safe travels!!