Big Tank, Big Fuel Reserve

I own a 2000 Ford Econoline passenger van with a 4.6L Triton V8. With the default Overdrive option enabled (as opposed to off for towing, which you have to set it to manually), it does very nicely. It gets a minimum of 12 MPG city/16 Highway, when it doesn't do better. The empty mark is hit with 5 gallons left in the tank (I've filled it up here several times and always end up putting roughly 30 gallons in the 35 gallon tank when I do). That gives this sucker a good 60 or more miles after being "empty"!