I have an older 2500 that has a max tow of 14,9. funny how newer ones have less. Anyway, my 40' toyhauler says 12,3 dry and I've had it to 15,9 fully loaded with fuel tank, water, etc. I was over the max tow, right on max of truck payload, and not over GCWR. I would not have felt comfortable if I didn't have an exhaust brake for hills but otherwise it pulled just fine. When I've had to go across mountain pass then I would drain the fuel/water to get closer to max. If I was pulling often then I might reconsider but we're fair weather summer campers so the amount of time has been minimal.