I am looking at 150s now and keep asking this same question. My uncles 01 4.6 gets 19 to 20 (hes 70), my neighbors 02 5.4 gets exactly what the epa says 14city & 18hwy.

Ask me, they all beat my 7.3 which cost $5000 more, gets 14mpg and costs 20c more per gallon for fuel.

check out the fuel mileage experiment, I think a few people claimed 20 there.

 

Good point check your odometer with those tires it's probably off. Clean your TB my mileage went from 13 to 15 in town after I had a full fuel system cleaning and replaced a few things. It's like a new truck, haven't had a chance to get on any open road yet but I'm sure it'll do much better than the 16 I've been getting there. The 5.4L is a good engine if you maintain it, they're not a dog