About to pull the trigger on this combo. Thoughts?

It sounds to me like you're in the safe zone. If you load the TT to the max (7,740#), and have 15% hitch weight, you'll be at 1,161#. That leaves the remaining payload for the Chevy at 644#. As long as you are careful to not put more than 644# in the truck (passengers, cargo, etc), you should be okay.

Of course, you may likely not hit the GVWR on the TT, and you're hitch weight may be less than 15%, so you likely have some buffer.