Got a surprise here as well, when I recently weighed my combo.
Trailer, loaded with most everything we take, minus food, came in at 5920. UVW listed is 5260, so we're doing pretty good on limiting the weight of the stuff we take along. The 5920 does include a load of firewood on board in a storage compartment.
Tahoe weighs 5860. This is with the 3rd row seating removed and just me on board. Maybe add another 200 out the door camping.
Combined weight of the Tahoe and trailer was 11780, well below the 13000 GVCW listed in the owner's manual. There was no water on board, since I rarely travel with the water tank full. But I'm satisfied that my combo has over 1200 lbs to spare.
On a sidebar, a place to consider getting your weights done -- Landscape and Garden Supply Yard, one of those places that sells bulk soil/stone by weight. I was in one the other day, noticed their scale out front and asked if I could bring my rig by to get it weighed. They said "sure, no problem", so I went home and brought the combo up. When I was done, I asked them how much I owed them, they said "nothing!". They had my business before this, now they definitely have my business.