If you have a Scan Gauge set it to GPH (gallons per hour) when you let off the gas completely to coast you can see it drop down to around .4 gph. About where it sits at idle. On level road at highway speeds I usually see around 3.8 to 4.5 gph. Put your foot in and you'll hit 10 to 13.
The keep MPHs highs, the GPHs low and you'll get good MPGs.