Sounds like this is a done deal and you now have both units.
The critical thing that has been pointed out is how much you are going to put in the truck plus how you load the trailer and how much you put in it. You will probably be (without weight slips) one of those that has to watch what they put in the truck/trailer and leave something behind if it's very heavy.
I am not familiar with the new 5.3 with 8 speed but figure it will be up to the task for the trailer - maybe not love the mountains, but do an acceptable job hopefully. Personally, I can't imagine pulling a 7800lb trailer with a 3.42 ratio (gas) BUT I'm hoping that 8 speed can help it out; but, a 3.42 is a 3.42.
You need a good quality WDH with sway control - absolutely. You also need to upgrade the P rated tires on the truck to LT. Take it on a long trip on some of our somewhat bumpy highways; I think you'll find that you want to add airbags for stabilization too.
You have the combo now so go use it being careful of how much you load where. When you come back from that long trip hopefully they will be having a sale on new HD trucks in your area........
