I had the same concern when getting my new truck. I got a 07 with a 5. 9 auto (48re) and it works outstanding with a new Torque Converter, Flex Plate, Valve Body, and Smarty. Much nicer than the Stock 6. 7 I test drove. I figure that with the 5. 9 I can go crazy with mods in the future and still pass emission tests.