So I picked up a new(to me) 05 SCrew with the 5.4L and was expecting horrible gas mileage... so I decided to give it the best chance at decent mileage by doing some basic things for it...
1) Fresh oil change
2) Replaced the dark grey colored air filter
3) Replaced the fuel filter(poured coffee colored liquid out of the old)
4) Ran a bottle of Lucas fuel treatment through it
5) Took off and completely cleaned the throttle body(was surprisingly dirty) and cleaned the MAF sensor
6) Did the Gotts mod
7) Reset the computer
8) Made sure tires were properly inflated

...my results... 17.7MPG 90% hwy driving..... with the 5.4L
Not bad for stock(except the gotts), and NO tuner.
So my friends, keeping up on simple maint. can help you at the gas pump!