This issue was discussed in TDR some time back from guys that had them and those looking at them. They all agreed the '13 2500/3500 SRW had the same frame
Some differences in looks and base weight numbers are in the FAWR numbers.
The 2500 2wd/4wd both use the 5500 FAWR as does the 3500 SRW 2wd models.
The 3500 SRW 4wd trucks use a 6000 FAWR.
I'm looking at the specs now and the 2500 4wd base weight is 7597 vs 7880 base for the SRW. Thats 280 lbs difference and IMO is to be expected.
And of course the '13 3500 has the bigger/heavier 7000 RAWR which adds to the trucks base weight.