i have a 1997 chevy it has a 350 vortech engine 150k miles through out the car i have put in hypertech chip airaid cold air intake airaid throttle boddy space and flowmaster snugtop in the back its not raised and do not have big tires on it and im getting around 11 mpg im not going over the speed limit and im not over doing it on the peddle what could be causing this bad of gas mileage or is this what i should be expecting from this truck ?