There is also a camper loading information sticker inside the glove compartment. It will tell you the maximum weight of slide-in camper that GM recommends for the truck.
What I can tell you is that you will almost 100% for sure be overloaded. That in and of itself is not necessarily unsafe, though. Your truck can be VERY unsafe, completely empty, if driven recklessly, or if it has extremely worn tires, or rusty brake lines, or worn-out brakes, or sloppy steering linkages, or bad front wheel bearings, or broken springs, or, or, or...
Assuming that you are a safe driver with a good head on your shoulders, and the truck is kept in tip-top shape, you can decide for yourself to take the risk of running overloaded. It would be a good idea to get upgraded tires with a higher load rating, and some sort of suspension add-ons.