GM does a very poor job of letting you use their website to sort of hone in on a payload range based on trim levels from what I've found. It will give you a benchmark for a particular drivetrain and cab configuration but after that it's just a guess so keep that in mind.
You've probably played around with their website more than I have but here is a link to a section of it where you can get an idea of what kind of payload you might be looking at based on truck cab/drivetrain configuration;
https://www.chevrolet.com/trucks/sil...tyleTwo=413332
Pick the basic truck (configuration) then look at trailering and payload under capabilities.