Oh well, I'm always appreciative of anyone who will give some good advise.

The Envoy has electric fans on it. I did the modding to that thing before the aftermarket supported it. 3.5 inch cat back exhaust that I welded up from some mandrel bent pipe with a 3 chamber 50 series Flowmaster, 3.5 inch intake pipe with nice filter, e-fans, and a nice tune. It knocks down 24 MPG on the freeway and about 17 in town. This is a 5.3 v-8 not a 6. The best it did stock was 11 in town and 17.6 freeway. Almost 2 MPG just from the fans!