gas problems

When I bought the truck 7yrs ago I got about 250 to a tank and its went down hill ever since. Iv got new NGK plugs Beldin wires rotor button,cap have never replaced the ignition coil, so if the primary or secondary in the coil was breaking down could that affect my gas. now since the control module was on the original breather housing do I need to hook up some other kind of module to make up for it