What exactly are your performance expectations? I have a 3900# dry camper which I have pulled with a 1999 F150 with the old Triton V8 and a four speed tranny as well as a 2014 F150 ecoboost. We got over 3000 ft mouuntain passes and from Seattle to Yellowstone and back just fine with the old truck. A little noisy at times running uphill in second gear with the pedal all the way down, but never broke down or overheated or anything. The ecoboost, well I can run in the fast lane with the best of them if I want to. Most of the time it hangs out around 2k RPM when towing. But that's a turbocharged engine that can burn arbitrary amounts of fuel at any RPM.
Point being performance expectations vary ... You should not have any issues towing with a 6L V8. I don't buy into the hot rod argument, they put it in there it has to perform to spec. The turbo AND super charged 707HP 6.2 Dodge Charger Hellcat is a hot rod. I am willing to bet your mill makes half of that.
Oil and transmission cooling should be available aftermarket as well.
The ECU should not let it knock, and in another vehicle I owned if it did, it would log an error. I'd get a free OBD2 readout at an auto parts store.
