those magnum, keg style intakes do not like rpm's for efficiency. About 1800-2000 is about were it needs to be to get fuel economy. 2200/2300 ish rpm, fuel economy drops of quick.Maybe an aftermarket intake is better? I have no idea. I've had a few ramchargers. 77 360 2 bbl,82 360 4 bbl,93 318 magnum. 10 -11 mpg is all they ever got. my 2000 quad cab Dodge dakota with 360, auto 3.91 gears and 31 inch tires. all factory and stock.10.6 mpg is my overall average. My over head console w fuel economy shows about 16mpg's at 45 mph, 70 mph is about 11/12 that is around 2300 rpm.