Ray, I had a 2002 GMC 2500HD with the Duramax and I had problems with the injectors that caused excessive smoking at idle. This is a known problem with the LB7 and GM extended the warranty on these injectors to 7 yrs/200,000 miles. I started having problems at around 96,000 miles and after a couple of trips to the dealer and trying a couple of different additives they finally relented and replaced all 8 injectors at about 123,000 miles. Problem solved; for a while. The "new, improved" injectors didn't last as long as the originals. I started getting the smoking again at around 195,000 miles. When I went back to the dealer they tried to tell me the warranty on the replacements was only 36,000 miles and I said, "Your kidding me, right?" After I, personally made several calls to GM they finally agreed to replace the 4 on the left bank (that seemed to be causing the problem) because I reported the problem before the original 200,000 mile warranty had expired. By the time I sold the truck with 219,000 miles on it, it was starting to smoke at idle again. I suspect the 4 on the right side were going out. Since you have an '04 model I would suggest you hurry on down to your dealer and see if you can get in under the 7 yr warranty limit. Good luck.