I once got 420 miles out of a tank of gas in my SVT, but I was REALLY pushing it, couldn't find a gas station for miles..
I averaged 320-350 miles per fill-up on the highway, and anywhere from 225-275 in the city, depending on how I was driving..
Ray - Might be time to replace your fuel filter, and clean your air filter, if you're getting such bad mileage. And maybe a bottle of fuel injection cleaner while you're at it.