Well depends on which motor right? You know a 2500 will cap at 10,000 lbs GVWR regardless of motor. The SRW 3500 will vary a little bit with gas engines (getting something like 10,400 GVWR) while comparing diesels, they up the GVWR to something around 11,400 lbs or so.
So if you're going gas, you gain only a paltry 400 lbs or so in payload typically on 2500 vs 3500. While with diesels, you gain about 1,000 lbs more payload because of the higher rating. Not sure why GVWR's tend to be lower on gas motor'd trucks but it's just my off-the-cuff observation.