Very impressed with gas mileage

mid 20s with 79 short bed 833od and idk gears, 4020 lbs, stock holley 1 bbl,stock electronic ignition, everything far as i know, when its cold dose lope a lil but if it ant stock it ant much more than stock! i got 2bbl and intake, split manifold for duel exhaust, and collecting parts for gm module mod but ol truck runs butter smooth, if it ant broke why mess it up?