I know my post wasn't helpful, but I think you should be able to do better with the gear you have. You didn't give much info as far as size of engine and compression, etc. What carbs are you using? Ethanol gas won't give good milage also.
I'm guessing that's about what I'll be getting also. At this point, after the lengthy build, I just want to get the 330 on the road, and use it before they are Deemed "illegal"...Remember with the cross ran you are running on 4 barrells ALL the time! My MAX is set up with 13.5, 3705 carbs, 4.11 gears, manual shift TF, no vac advance and 28" tires. I tell people I get 5 MPG. Maybe not even. When I punch it I do watch the gas gauge drop! It is WAY too hard to keep your foot out of it. And I am running 110 octane leaded at about $13 or $14 a gallon! The 3705s are supposed to be 750 CFM.