Well I'm not an expert in the 5.4s because I only have a 4.6L with the 3.55 LS. Those numbers that you posted are pretty close to the same mileage I get. My daily trip may include 3-9 miles of 55 or so mph on backroads followed by about a mile or two of stop and go city driving that has about 10 lights that prefer to stay red...not to mention multiple railroad crossings but I usually beat the train.
That trip will average 13-14 regardless of my driving habits. No joke, driving nice or pedal to the metal its all the same
.
How does that compare to your driving?