I got 19 mpg on my way home from the dealer I bought my 07 from. Been downhill ever since with bigger tires and lift.
34"s and maybe 4"-5" of lift.
Regeared to 5.13's 100k ago to stop hunting so bad on hills when loaded for camping w/ RTT.
Like other posters have said, a bit of poor mileage is a small price to pay for reliability and mine has been through some tough times as a work truck.
All that being said, I can definitely testify that there are all the available gallons in the tank for using. The Tundras are famous for having gas hand problems, indicating empty way early, but the gas is still there and useable. Many owners are totally used to reseting the miles and mpg every single tank fill so they can know exactly where they are when the tank gets low but the hand says empty. The tank being so small and short range already makes it pretty annoying to have the hand indicate empty when there's a quarter tank left. I solved the gas hand problem when I needed to drop the tank and put in a new pump.
I could get 14-14.5 highway driving if I kept it below 55. So that never happens. I do a lot of start/stop for a couple miles down dirt roads and will get 10-11, and normal driving my all around average is 12.5.
OP, does your dash not have an average and an instant readout, even if it isn't in George Washington's thermoses per football field the way God intended?
Tank refills aren't accurate enough to work with IMO.