Heres some looking around info. Stay away from the '01 - '04 LB7, injector problems. Easy way to tell feed lines and wire harness goes thru valve cover for injectors. '04.5 - '05 LLY Some were prone to having cooling problems. '06 - '07 LBZ best one in my opinion. First year for 6-spd allison the others were 5spds, you hardly ever hear of injectors going out, which are external from this year and up, and from the factory came with 365hp/610tq. '07.5 - up LMM good engine little more power from factory but stricter emisions(dpf, etc...). Some early '06's like mine were the LBZ engine with the '05 engine tune cause the emisions did not get certified in time for production, but a good tunner either handheld or custom will get you where you need to be. My truck when I had the PPE tunner on lvl 4 which was 225hp I made 452/900 @ beans in Dec. and that is borderline where you want to be w/o a lift pump and better built trans. You can look in the glove box to find out what engine is in the truck the code sheet is laminated in there and they are alphabetical. Just food for thought!:thumb: