You're not going to notice the difference between a stripped down 2 door weight and a loaded 4 door. And provided your comfortable with the power your truck has now, it won't be a lot different.
The biggest thing is the toad or trailer will not be providing and wind resistance to the equation because the camper is already doing that for the whole setup.
Just got back from a trip with the camper, towing an almost 7000lb 10' tall boat behind. I notice virtually zero difference if it's just the TC or TC and trailer. Granted I've got over double the torque as your GM, but it's all relative. I get the same mileage and drive it the same trailer or no trailer.
Comfort levels are different though and if you're questioning your choice of engine after loading a big camper on your truck, then towing virtually anything will dog you down.
For comparison, friends have a V10 Class A that they towed their Wrangler behind. Similar engine power and wind resistance. Different becasue the A is better setup for towing than your dually, way deeper gears, but same thing, said he drives the same, about the same mileage, toad or not.