Given the fact that engine tuning is largely a constant factor now compared to the old days of carbs and crude throttle body setups, mpg will not vary much from (similar) vehicle to vehicle under the same conditions. That 6.2 also has very similar power numbers to any of the HD gasser trucks.
After 30+ years of towing 100s of different trailers with 100s of different trucks both 1/2 ton and HD and gas and diesel, I can tell you this question is largely pointless.
Within reason gassers will get within about a mpg of each other towing the same load same conditions. And diesels will do about 30% better.
Towing mpg should near or at the bottom of the list of concerns or considerations when choosing a truck, as the only real question is gas vs diesel if you’re looking at mpg.