i aint no chevy guy but i know of a few big D's that dont run half bad, look at the other duramax threads, and if you want to bomb one go here http://www.crankitupdiesel.com they are the best when it comes to duramax's, duramax's run quiet, they get great mileage, 24 or 25 mpg stock, and make wonderful power and whats nice about them you can switch them back to stock at the flip of a switch just by turning of your box, reprogrammer or downloader, the 12 valve has no electronics so everything your gonna do to that truck is mechanical which means once the stuff is in there its there til you got to tear it down and take it out, now duramax's do have some draw backs, they wont last longer than a 12 valve cummins because they aint designed as industrial motors like the 5.9, they have head gasket problems with extremely high boost levels which are fixed with head studs and they have weaker main bearing webs and cranks on the 2001 to 2005 LB7 and LLY motors but this is only when you get upwards of 60 pounds or more of boost and are running a pretty hot "program" on them, but the new LBZ motors fixed all those problems in the 2006 model year trucks, if you want a quiet strong running motor that pulls great, can easily be modded get a duramax, a 12 valve is cheap to mod also but they are loud and get crappy mileage, but in the end its all what you want, DO NOT GET AN AUTOMATIC IN ANY OF THE TRUCKS YOU ARE GETTING, THEY ALL SUCK.