The trim piece says 1500, mine is a 1/2 ton, not a 3/4.
Ok. Then IOKKI has the right numbers for your vehicle after all. The highway mileage difference may be due to the California emissions package, which the 49-state versions (obviously) don't have, and which probably rob you of at least 10 horsepower. I'm betting you still only get 8-10mpg in the city though, even with the 350 (5.7liter). You might consider trading up to a 3/4-ton, with a diesel, especially if you tow. The 1/2-ton can tow that 2-ton horse trailer, but your rear springs and transmission will not thank you for it (you do tow in 3rd, not overdrive, right?).