What can a Chevrolet Silverado / GMC Sierra 3500HD (Duramax DRW, gooseneck) ('20-26) actually tow?

The rating is the easy half of the answer. A trailer never weighs its brochure dry weight — water is 8.34 lb a gallon, propane and batteries ride along, and so does your gear — and hundreds of models changed their published weights mid-run, so the model year decides as much as the model. Judged that way, with a 10% margin and 2 people aboard: 5150 of 5150 campers fit a Chevrolet Silverado / GMC Sierra 3500HD (Duramax DRW, gooseneck).

The number that quietly binds is payload — 6,644 lb (Regular Cab Long Bed DRW 2WD, Duramax 6.6L, 17-in wheels - the config rated 36,000 lb gooseneck; the 6.6L gas in the same body is 7,290 lb): tongue weight lands on the rear axle with your passengers and the hitch, so a vehicle often runs out of payload well before it runs out of rating.