Your calculations appear to be correct, Harry. My 2015 has a GCWR of 15250 so I can tow up to 4220 so long as I don't exceed the tongue weight limit.
As an aside, I just made a 1960 mile round-trip to Montana and back pulling a horse trailer, empty there, with a horse and llama on the way back. With the animals I figure I was pulling right at 4100 pounds. I kept a steady 65 MPH, except when climbing steep passes of course, and mileage ran between 11 and 14 mpg. Naturally the segments with high mountain passes were the ones with the lowest mpg.
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