2001-2004.5 Trucks had the LB7 Motor 5-spd auto. These motor's had injector issues. GM did warranty them to 200k miles though.
2004.5-2005- LLY motor 340hp 5-spd auto. Had an overheating issue (which was more talk than really an issue with most trucks, but the LBZ mouth piece in and issue fixed)
2006-2007.5- LBZ motor 365hp 6-spd auto. Try to get a Pre-emissions truck (early 07 and down) because with the particular filters and emissions bullshit it kill the mileage. Motors cracked pistons at higher hp and tq (if it's turned up).
LBZ is the best motor you can get in stock form. As well as the trucks. And you get the 6spd tranny. 06+ trucks came with tow mirrors.
http://www.duramaxforum.com/forum/general-discussion/61741-read-first-before-posting-please.html
Pitman arm's are weak. The allison's hate EFI live or any high hp programmer.
I have a good deal on a 2006 LBZ right now. Crew cab, short bed, white in color. 128k miles. Runs great! 15.50 1/4 lol! $24,950
http://www2.diamondlot.com/dls/inventory/standard/detailxsl.aspx?id=1483795&lang=en
I do have a couple d-max's right now. http://www.thecarcompanyonline.com