That being said, I wouldn't consider the ST a "truck."
I had a 2000 F-150 5.4L V8 and it got 15-16MPG regardless how I drove it (city, hwy, mixed). I had hoped or assumed (didn't research it like the original poster is) that the 4.0L V6 would get much better gas mileage. I was wrong. It's marginally better. My 2001 gets about 18 - 19 MPG mixed driving.
Don't get me wrong. I LOVE my ST. If you're looking for a truck for cargo and/or hauling. I'd look at the traditional pickups. I sometimes miss the F-150's load capacity. If you want a fun vehicle that can do a little of everything (a little hauling, cargo, passengers, off-road, fun to drive, easy to park, etc.), the SportTrac is great!
Happy Hunting!