My current setup is a 2011 Sierra 1500 with 5.3 and 3.42 with a payload rating of 1420 lbs.
I pull a 30 foot dry weight TT of 4370 lbs and scale measured for a full trip at 6006 lbs. My tongue weight is around 900 lbs and I use a Husky WDH with 800-1200 lb bars. I wasn't happy with the amount of bounce between the truck and trailer, so I added a pair of leaf springs to the Sierra and everything stiffened up nicely.
I only use gears 1 through 4 for surface streets, and sometimes I use 5th for flat freeway driving. If I don't keep the revs up then I start experiencing high transmission temperatures, bad fuel economy, and it barely pulls when I want pass or speed up. When keeping the transmission in a lower gear and the engine revving higher, my fuel consumption gets much better and my transmission temperature stays low.
Remember, 5th and 6th are overdrive in the 6-speed Sierra.