I'm a real rookie with this whole diesel thing. Since buying my first diesel in March, a 2004 GMC 3500 DRW CC SLT 4X4 LLY/Allison, I've been trying to get used to the way diesels perform. In addition, I'm trying to readjust the way I think and change some of my old habits like remembering to look for stations with diesel fuel, waiting for the glow plug light before starting, etc. In addition to that, someone has told me that it is necessary to let the engine "idle down" for 30-60 seconds before shutting off the key. I can't find anything about this in the owner's manual but, since that time, I sit in the truck for about 60 seconds before shutting it off. Is this really necessary, is it recommended, or am I the victim of some kind of "let's mess with the new guy" diesel humor?