My 2018 Tundra with the 5.7 is averaging between 14-15 over hill and dale in northern VT/NH. Towing the boat (5500 lbs wet on a trailer) drops this down to 12.
I was actually doing a bit better (by a whopping 1 mpg) at altitude when I was still out in Jackson. I'm thinking less O2 at altitude meant less air fuel mixture so saved gas. That and some long downhill runs off the pass to juice the numbers. That said, I seem to be at the top end of the spectrum in terms of mileage returns.
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