The duramax injectors are extreamly sensitive. The holes that the fuel pass through are about the size of a human hair. Id say stick with injector cleaner if you want to add anything. If you read the owners manual it actually says NOT to add any additves
Alot of people who are use to the old diesels or even semi's will say that its a good thing to add oil or atf but these trucks are a whole different animal.
Heres a pic of the injector..
