I always wondered if stuff like that affected MPG that much, why wouldn't the manufacturer put it on there to begin with? Pretty sure a lot of testing goes into these vehicles. The guy probably bought the vortex, then went easy on the skinny pedal, then thought it was all the vortex at work.
Multiple places list it as doing nothing and Popular Mechanics listed it as making a car perform
worse on the dyno. Maybe it depends on the car. People get different results with CAI's on different cars.
I think driving habits influence MPG more than anything else. Scanguage II lets you see your current MPG so you can find out where your best MPG range is and what driving habits cause it to increase or decrease. I went from averaging ~15 MPG on long distance driving to being able to go to ~18 MPG on long flat trips with the V8 on 33's just by seeing where the sweet spot is. Plus you can monitor a lot more than MPG.
But at the end of the day, it's a Hummer and MPG isn't going to ever be amazing.
