If you never take it offroad, then I recommend getting road tires as it's more efficient. Otherwise get the most expensive off-road tires if you always go offroad. Never buy cheap tires.
Make sure your oil is clean and add STP fuel additives.
Really not much you can do with the already low MPG from a Tundra besides making sure it runs clean and efficiently.
If you want more power, I'd recommend you adjust/upgrade your suspension and turbocharge the engine!
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