TL*THE CONTACT OWNS A 2004 GMC SIERRA DORMAX DIESEL (NA). THE CONTACT STATED THAT THE FUEL INJECTORS PRODUCE WHITE SMOKE. OCASSIONALLY, THE VEHICLE BECOMES DIFFICULT TO START. THE CONTACT SERVICED THE INJECTORS EVERY 10,000 MILES, BUT THE FAILURE IS PERSISTENT. THE VEHICLE WAS TAKEN TO THE DEALER AND THEY KEPT REPLACING THE INJECTORS, BUT TO NO AVAIL. THE FAILURE MILEAGE WAS 30,000.