I'm pretty sure the GVWR for the 19 GM 3500 srw is 11,500. The new 2020's, which are supposed to start hitting the dealerships this week, will be 12,250 from what I've seen which should increase the payload capacity. I've looked pretty close at them, on line, and have been impressed with what is being offered. There is a down side: more money and I would not really want an early production model.
Look at the little yellow sticker on door pillar and it will tell you the payload capacity for that particular truck. I really don't like driving a dually either but I could not find a truck in a srw equipped like we wanted that would handle the close to 4K pounds of weight we add to it. We have about 3100 pounds of hitch weight which the factory said was 2685. The rest is us, a fat Boston Terrier, 25 gallons of extra fuel in a transfer tank, the hitch and other odds and ends. It adds up quick once you start putting your stuff in it.