We purchased a 2007 379, with a 550 CAT we drove it home and was fine the next day noticed it was Idiling rough. Long story short after 4 loads we have had a complete over haul on it due to a cracked head. After new head, cam shaft, crank shaft, all new rocker arms, one injector, liners, pistons, wiring harness, alternator, fuel pump it is still idling rough. It runs like a beast, doesn't cut out when running down the road and will even idle up and not cut out. Not throwing any codes and even the CAT dealer didn't find anything when they checked it out. Timing has been checked, changed fuel filters, next is going to be throttle position sensor but out of the 4 mechanics we've had it to all of them are dumbfounded in what it could be. The motor has been combed through over and over and nothing has been found. If anyone has ever experienced this please HELP!