Will,
Have you actually weighed your rig combo at a CAT Scale? If not, go weigh your set up so you know all your weights, including the tv ra weight. Have you add any accessories to your Chevy: step bars, tonneau cover/truck topper, etc?
I ask because we had the (almost, not sure if you have 4wd or not) same truck as you towing our last tt at ~7200lbs/ ~910lb tw. Our '10 Chevy 1500 CCSB 4x4 5.3/3.42/6spd was about 200lbs over the gvwr, but only 50lbs UNDER the rear axle rating.... We did have a cab high fiberglass topper on the bed, spray in bed liner, and that was with a tool box, 4 bikes, and I think a cooler in the bed. As you can see we now have a 2500HD as a result, which ended up with us buying a larger trailer.... So depending on just how you load you may actually end up being over more than you think, and possibly over the RAR if you don't know your current RA weight when loaded for a trip.
I did have a set of LT LR C Cooper A/T3's which were way more stable than the factory p rated tires. But being over the GVWR and very close to the RAR we decided to step up the HD.
Did you install the 3.73 gear set? If not, it was my understanding that only the Max Tow trucks with the 6.2 had the 3.73's. The 5.3 trucks had a max if the 3.42's.
I will say I never felt we were lacking power when towing ~7200lbs, even when we were loaded a little heavier (in the tt) for our big trip. But that is here in Michigan.
In regards to what is an ok amount to go over the ratings, I have found everything posted from "There is at least a 50% reserve capacity above the raging" to "The margin of the rating to the breaking strength is not as much as people think":..... Only the manufacture and the engineers can say for sure, which I am guessing they will never tell.
Good luck in your decision as only you can decide what is safe for you and your family!!!! But please remember to Include all of our families in that decision as well.
