I am considering getting out of my 6.0L 1500 to upgrade to a Duramax with a crew cab. What I am concerned about is what the current crop of Duramax engines are producing in the real world for fuel mileage. What do you guys get from your trucks? What can I expect from a stock 08 or 09 Duramax? How much benefit would I see from adding a larger diameter exhaust and what would that cost? Also, I saw mention of "regeneration" in a few posts as I was doing research... what is that? Is that the cleaning process for the particulate filter in the exhaust? Thanks in advance for any information. I don't know much about diesel trucks (though I have had diesel cars) but I learn quickly so I am looking forward to any advice/help you folks can give me.