Getting better MPG 2000 Suzuki Grand Vitara V6/2.5-has 76,455 miles..

What is your question?

My MPG is running around 10/12 MPG around town,and at times less..I change my Engine oil faithfully every 3000 plus miles,ck tire pressure often,new air filter,no hotrodding....My question also could the Gas Cap be faulty?