I have a bit of a mystery with my 90 Fleetwood (4.5). The thing seems to be consuming more gasoline than its fair share. There is a minor problem with the fuel data center. It displays fewer gallons (especially upon getting lower) than are actually in the tank. However, this is not the concern, because I've heard this is the case on many of these models...including my friend's 93 Fleetwood. However, what is not so common is the fuel used indicator... It seems to be that at the pump, I have to pump a gallon more, give or take, than what the fuel used says was missing (regardless of how much fuel was used). This sort of leads me to believe a leak could be there...though I have looked under the vehicle several times and seen nothing...perhaps that is not a sufficient inspection.... Anyway, taking that phantom gallon into account, the bloody thing only gets about 21 MPG on the highway. Yes, it's a V8, but I have read that these engines are capable of far better...such as the aforementioned friend's 4.9, which gets about 28. I just replaced the thermostat, in case it was the engine asking for more gas because that was stuck...no difference. The fuel filter looks average...and I do not believe that or the fuel pump would be the problem, because there is no lag and the car accelerates just fine. I took a plug out, and it looked a bit white (engine running a tad hot), but nothing to warrant that steep of a mileage drop. The wires look gorgeous... I replaced the air filter, the tires are properly inflated, the engine is not using oil, the catalytic converter is only 2 years old, and I'm clueless . Oh, and the car has about 117K on it, and yes, I use 93 octane. As I said, aside from at the pump, the car seems to be doing just fine, making diagnosis a veritable nightmare. Anyone have any ideas, it would be greatly appreciated.