I have a 2001 Duramax with 99,000 miles on it. Early on I took it in to several dealerships to check out a surging/ fluttering problem at idle. The most I got out of the mechanics was that it might have an injector that was a little weak, but certainly not serious enough for replacement. I've continued to hear about all these injector problems and horror stories after they go to working on the engines, so I'd just resolved to drive it until something bigger happened. Now the fumes from the exhaust have gotter particularly bad. The fluttering really isn't any worse, but the fumes at the tail pipe indicate that the combustion is really poor at idle. What do you think? Should I take it to a GMC dealer or find an independent mechanic to work on it?