I have a 2005 Chevy 2500 HD with a Duramax diesel engine that I use for my concrete business here in the LA area. My Check Engine light came on last fall, but the truck runs just fine, pulls the concrete uphill every day, just fine. So I pretty much ignored the Check Engine light. All the fluid levels are perfect. No strange noises or excessive smoking, and like I said, plenty of power. There was no indication of a problem until I decided to drive up to the mountains to go skiing. The truck ran great on the way there, and started up fine after a couple of stops in town. The next morning however, it did NOT want to start! After cranking for about 30 seconds or so, it finally started, but it ran roughly and made a lot of clatter for a few minutes after that. What could the problem be?