why am i using so much fuel on 2001 Chevrolet Silverado 1500

i recenlty changed my spark plugs, spark plug wires, and the rotor cap but I am still using so much gas. every time I will have half a tank of gas go about 30 miles and I it is a quarter of a tank.

1 answer
Could be your fuel guage is inacturate,,,suggest you fill tank and drive till its near empty to refill and caculate your mileage on a compleate tank use.