My 2004 F-150 Heritage is absolutely devouring fuel. I am barely reaching 11 MPG. I mostly do city driving, but compared to what I've already read on here, that still seems 2-3MPG lower than it should be. Does anyone have any tips on how to boost me into the 13-14MPG range or better?

 

Assuming your truck is up to par mechanically, IE: tune up, air filter etc. etc.
The answer will probably disappoint you. Buy a newer truck! I have a 2004 Screw 4X4 with a 5.4 and what you are saying is about what I was getting.
I spent a fortune on mine to improve fuel mileage and towing. SCT tuner with 5 star tune, deleted the Mechanical Fan and fan clutch and installed dual electric fan kit, Stainless works long tube headers and full stainless dual exhaust with high flow cats, all synthetic fluids in diffs. trans. transfer case and engine.Every thing I did helped in both fuel mileage and performance, especially performance!
That being said 14 or 15 around town is as good as it gets. Ive spent thousands to get it! The only reasons I did this is my truck was paid for and only has 60000 miles on it. I did the headers primarily because I had broken exhaust manifold studs and the manifolds had to come off anyway. I have 2 friends who have newer F150's with 5.0's in them that do that with nothing done to them, and 18 to 20 on the highway.
Sorry to be the bearer of bad tidings!

 

Driving in the city is like drilling holes in the gas tank. My '06 4x4 4.6 gets about 9 mpg when my wife drives it in city traffic! I get about 19 mpg on the highway and 12-13 in town when I drive it...