Again, blah blah blah ... Why do you need all the power of the engine?) to tear the trailer apart?))) You lose the thread of the conversation, you are constantly trying to take it aside. About miles per gallon, I showed you clearly that I can easily get the same figures at 6,2 ..you have only words and words all the time .. No photos or evidence)))
Dura Yuk is correct about this one...as it relates to torque.
To tow you need torque, esp when going uphill. Diesels are at max torque at the low range of their RPM's, for a gasser, you usually have to get up in the RPM's to get the max torque...so, in those cases, the automakers usually tune the shift points in the transmission controls accordingly.
Suggest doing a YouTube search for TLF Truck "IKE Gauntlet"
Those guys tow at max load up a very steep mountain grade, and do it with most all of the powertrains available in most brands of trucks.
They tested both the 3.0 Duramax and the 6.2L in both GM Pickups and in the SUV (not sure if they did the duramax in the Suburban/Yukon) or not. They measure MPG, engine braking, noise, the whole gamut....it is very enlightening.
Diesel will almost always win in a towing competition, and a fuel economy competition; because the characteristics of the engine deliver peak torque sooner, and because diesel fuel has a higher energy density than gas.
The gas engine will put way more smiles on your face if what you like is acceleration. Both have their purpose...and it is personal preference and application as to which works best for a given user. This is why GM offered a choice in the powertrain.
I drag my 4500lb boat trailer all over the place (before was w/ a 5.3L in my 2013 suburban, usually to the tune of 12-13MPG, and now w/ my 6.2L Denali, usually to the tune of about 16MPG) we have hills and such around here, and some interstates I drive on w/ the boat I need to be at 70-71MPH to not get blown off the road by other traffic. I suspect the 3.0 duramax would do a little better than the 16MPG, and know it would be great when not towing...I chose the gas for the fun factor...and I am not disappointed. If my lifters blow out my valvetrain, I'm blessed becuase my dealer "included" a lifetime powertrain warranty...so aside from some downtime, I'll be whole in the pocketbook.