I've came across a 2004 silverado RCSB with a 6.0 iron block stroked out to a 408 with a turbo on it and it has a 4L80e trans. I know gas mileage would probably be around 10-12 mpg in town but I wasn't sure about highway.. I mean as long as you don't get on the throttle too babd, overdrive should give you a decent number right? maybe 18-20 mpg? The truck has been dyno tested and has two turbo settings: low, (6 psi, 520hp) and high (18 psi, 667). Assuming you keep the boost down low, would this be a good daily driver? Any thoughts or opinions would be appreciated. Thanks.