Mike, that sounds about right if you drive with a heavy foot like I do. I did a fuel millage test a while back and the results are in the thread
http://www.motorgen.com/forum/showthread.php?t=522. However, just know that in these tests I was very light on the throttle. I don't think I ran the rpms up over 2500 or so during the whole test. I've also checked my mpg a couple times with a combo of city and hwy at my normal driving and if I remember correctly it was somewhere around 18-19mpg.