I would say my overall avg runs around 17-18, but I drive 90% city stop n go BS
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Idk if the 09-10 do it, but if u hold the ok button on the steering wheel before you start an 11-12 it will give you a whole ton of program versions and jive one of which is lifetime mileage for the truck.
As far as the lie-o-meter: mine is usually within 0.5 from hand calculation.
I was simply reiterating my point from earlier about getting 27-28 cruising at 55mph