My 340 getting 6 mpg

6 mg ? no idea what is wrong but that is bad stock my 340 got 15 to 17 mpg 323 gears now getting 20+ with gear vendor and 3:55 gears . Even my 426 stroker got 9 mpg . Those 3:73 gears don't help much . With the right parts and tune you should get 15 mpg