Seems the best way to increase mileage is with the SCT you already have, keeping your foot out of it. I have heard the Snow system is awesome and can increase a few mpg's. Maybe 1-3? I read something recently on the Snow system about mileage increases - but dont remember what.
I dont think though - that all these mileage increases are "stackable". You know - like a 2-4mpg gain with a looney tune and foot out of it, 1-3 with snow, 1.25 with right oil (I got a 1.5mpg increase with rotella 5w40 synthetic), etc. If that was the case - we could all have 30mpg trucks!