I wouldn't trust the payload ratings in the brochures as they don't deal with a specific truck with specific options. The best way is to take the GVWR rating and subtract the weight of the truck. For example my 3500 DRW is rated at 12,000 lbs GVWR. I haven't weighed the truck yet, but expect it to be about 7,200 lbs, which gives me a payload of 4800 lbs. I believe the 3500 SRW is rated at 9,900 lbs and a 2500 at 9,000 lbs?
Just to illustrate, using my example I have 4,800 lbs payload capacity (including driver, fuel, dirt, etc. )
A 3500 SRW may weigh 200 lbs less, so maybe 2,900 lbs.
A 2500 would weigh about the same as a 3500 SRW, so probably about 2,000 lbs.
Disclaimer: You must weigh the truck to get the exact numbers. Ignore the published vehicle weights.
Cheers,
Dave