Diesel Bombers - 06 dying for no reason

My friend has an 06 dodge w/ 166k on it. He called me yesterday and said his pickup just shut off for no reason and now wouldn't start. It would just turn over and over. So my first thought was injectors. Well went down there to look at it and I saw nothing really out of the ordinary with that. It had no codes but I figured I'd go ahead and erase any "ghost" codes. Well, I used his smarty sr. to clear the codes. It also updated the ECM. After that it started right up and he drove it around and drove it home. Today when he got off work it happened to him again. He cleared the codes and it started right back up and is driving again. I told him to undowload the smarty to see if that helped. The smarty sr. and straight exhaust are the only mods to it so far. Also the tach is messed up on it but he said it's been like that ever since he bought the pickup. I believe it's a defect in the 06's. Anyways does anybody know of anything else that it might be if it's not his smarty? sorry for the long post