100K mile Duramax

You need to find the old man that barely drove his truck, and was meticulous with maintenace. They are out there. Those seem to be the best trucks. The ones you want to RUN from, are the younger guys with a cocky attitude. They seem to be the hardest on their trucks and always have something to prove. If you see the truck smoking white at idle, that means the injectors are toast. If it smokes a little black/gray when you stand on it, that's fine. Injectors cost about $5k to replace, so figure that into the price if that is a problem. Have a GM Dealer look the truck over thoroughly before you fork over the money to the seller.