What does the tornado thingy claim to do? Swirl the air so that when the air hits the combustion chamber it mixes with the fuel better to get a more efficent burn, thereby increasing your gas mileage and benifiting from more power. You drive a chevy truck with a VORTEC engine, an engine with a head already designed to swirl the air entering the combustion chamber, so no you do not need one, your motor is already doing it for you.
The Tornado has nothing to do with more air, or more fuel. It was designed on a very sound basis for airflow into the cylinder, but executed very poorly. In most cases by the time the air that has been 'swirled' by the tornado reaches the cylinder it has already smoothed out again because of the distance it has to travel and various other devices that stand in it's way affecting the airflow, ie throttle plates/butterflies and intake valves.
You start with a bag full of luck and an empty bag of experience. The trick is to fill the bag of experience before you empty the bag of luck.