I have a 23 ft travel trailer (gvw 4360 lbs / gvwr 5500 lbs) I plan on towing it with my 2006 GMC 1/2 ton truck SLT 5.3 Eng. with the towing package, also installed in the truck are the trailer brake ...
First, if my Ford 5.4 can do it lugging along with the 4 x 4 crew cab that's attached to it, so can you with your GM.
The best thing I could suggest is to load it up for a weekend camping session, fill the tank, and drive it to a scale. Have fun on the weekend and then assess the ride and feel of the tow combination.