Here are some numbers for a '13 3500 SRW LTZ 11600 GVWR 7000 RAWR Dmax/A long bed 2wd from GM online ordering guide. It has a 17300 tow rating and a 4464 payload as configured per the weight calculator.
GM Online Order / Reference Guide
The weights calculator gives the trucks payload and tow ratings for that particular truck as its optioned out. Neat feature.
Your trucks payload and tow rating will vary from these numbers according to what its base packages are and its options.
One thing about a TH is the pin weight can get lighter as toys are added in the rear of the trailer.
We have a TH forum and there are several TH websites. Do a google. These folks will probably have the same combo your looking at.