In my 2011-5.3 Silverado I just completed towing my 29foot-5,500 pound travel trailer around the U.S. The total towing miles were a little over 8,000. It has the 3.42 axle and did just fine. I had ZERO issues with the truck as well as the trailer. FYI-there are not any standards on how tow ratings are determined for specific trucks. The industry was trying to come up with some, but it hasn't gone anywhere. You will be fine with the 3.42 gears. Here is a little info-
http://www.caranddriver.com/feature...-sae-trailering-standards-explained-tech-dept
http://www.caranddriver.com/feature...-sae-trailering-standards-explained-tech-dept