I agree with CSG, that sticker assumes a 150 pound person in every seat in the truck. It also assumes you won't exceed the GVWR of the truck.
My own '05 Chevy dually has a sticker saying a camper can only be 3,469 pounds. My camper weighs 4,000 wet. I also have a custom aluminum flatbed on the truck full of tools. Add in my family and the weight of a trailer and the truck is about 1,600 pounds over the GVWR. I've got thousands of trouble free miles with this set up over the last 6 years. I added air bags, aftermarket shocks, and wider tires.
Staying within a truck's GVWR with a mid size or larger truck camper is almost impossible without a dually. Everything people typically want on a truck takes away carrying capacity: 4wd, diesel, crew cab, heated, cooled, power, deluxe everything. It all adds up.
