I have a 2013 Suburban, 2500, 6.0 liter engine, with 6,000 miles. I purchased it new in July of 2013. Since the vehicle turned 3000 miles, I've noticed that once the vehicle reaches operating temperature, there is a rough idle when stopped at a light in drive. I can see that there is a slight fluctuation in the tachometer reading which hoovers around 500 RPM. I can actually feel a vibration while stopped with my foot on the brake. I have brought the vehicle backed to the dealer twice for routine oil & oil filter changes ( 3000 & 6000 miles) and complained of the rough idle. Each time I was told that the technician had checked and found no codes and that since the check engine light was not coming on, there was nothing that could be done. One Service Advisor referenced a service bulletin that described a rough idle as normal. I purchase gasoline from branded stations, not the cheaper locations. I find it disturbing that this condition could be considered "normal". Has anyone else had this problem ? Any suggestions would be appreciated.