I can think of a few things at that milage. Check the fuel filter, if its orginal get it changed out as the regulator is in there and that manages the pressure in the rails which means if the pressure is low and not flowing well you will need more throttle input per given speed thus using more fuel. If it running lean the computer will dump some extra fuel to cool down the cats.

I speak form recent expereince as I had to replace a broken filter and fuel pump and my miles per tick on the fuel gage jumped up by 25 miles on the first notch on the tank from full. At that rate I will add nearly 100 miles per fill up.

The next would be a failing O2 sensor which may be causing the engine to dump some fuel to cool down the cats or correct a lean fuel mixture.