The myth of good mileage 6 cylinder Chevy's is absolutely true, not a myth! My '53 and '54 both std. 3 speeds got 16 to 17 around town, and always 20 to 22 on the road. My Dad and brother both had similar mileage. My '55 with overdrive always got over 24 on the road. I had stock Rochester carbs on all, with 56 to 58 jets. If you're not getting good mileage look to your ignition, wrong point gap will seriously affect mileage, should be .016 and timing set by ear to have slight ping when full throttle at low speeds (25 to 30) in top gear. Make sure your carburetor is clean, all internal passages clear and good springs and ball bearings in proper places, and automatic choke pulls off to no choke position as soon as engine starts. I also had good power for 6's, ran hard enough to beat many '55 v-things, low 16 sec. e.t's at near 80 M.P.H. (with Fenton Cast Iron headers and steel pack mufflers)