I am having the same issue. Sometimes the exhaust smells different to me when its idling. Last night I was at a traffic light stopped and I felt a bang and then again. I watched my tach and noticed with the bang my tach dropped almost like it was missing. It didnt throw any codes but I am very concerned for a $73,000 truck to be sounding like this with 18,000 miles on it. I will keep following this thread.