Is it a 2007 or a 2007.5 (new body style)? This is when they went to the DPF on the 2007.5 if I'm not mistaken. I may be wrong as I have been in the past and I'm sure I'll be in the future.
Also like stated above the newer 2013 2500 probably has more capacity than the 2007 as GM did a bunch of upgrades to the trucks. For instantance my 2011 F350 SRW LB gasser has almost the same GVWR as a 2007 GM dually. The duallies of that time frame were 11400# GVWR and my Ford is 11200# GVWR. The 2011 later Ford diesels SRW max are 11500# GVWR. I think GM was pretty close to the same. The 2007 is probably a 9900#GVWR and if equiped properly the 2013 could have a 10000# GVWR and is probably lighter than the 2007 Dmax. If you looked at a new 3500 you would probably be in the same range as the Ford of around 11200# GVWR.
I agree that the Dmax well have more power but that is not all you are looking at for hauling a TC. With my 6.2 gasser I can pull any hill that I have crossed with my camper running right at 60 to 65 MPH. This is not all I can do it is just the speed I travel with my TC on. I get between 10.5 and 11.5 MPG with it. It is true that I have to wind up the engine some to pull the hill but it makes it with no effort.
This is IMO