I have an '05 2500 QC SB that is tuned and I pull a 39-40' 5er (depends on where you hold the tape LOL!) that has a GVWR of 14,000# with a 4,500# boat behind it. I have a stock trans with no exhaust brake. I have factory 17" wheels with a little bigger tire on it and it does just fine.
I drive a heavy haul truck at work and my company vehicle is an F350 DRW CC and I can tell you that my Ram handles this load just as good as the F350 would ( I have pulled similar with it). I will tell you that my rear suspension is not stock. I am total air ride on the rear. The factory springs handled it fine it just squatted it more and had a little more bounce to it. Your helper springs would take care of that just fine.
I don't care what anyone says, I have pulling heavy loads for a long time and when you put 10-15,000# behind you, it won't matter what you have pulling it, it will drive and operate differently.;)