The V10 has been very good in the most part, I have worked on a number of them, and they are a petty bullet proof engine, but poor fuel mileage. A couple years ago had one come into our shop, 280000 miles, still had good compression and no oil leaks. My favorite combination is the Cummings hooked to a Allison transmission, but no body makes that combination in the smaller trucks.
As you have been told, sounds like you have way too much trailer for your vehicle. I read on here somewhere where your dry weight should be no more than 80% of your trucks towing capacity. 8000 towing then dry should be 6400 or less.