2006 4.0 automatic, 1300 miles, I am getting small muffled back firing during deceleration at the lower speeds, like when in slow traffic also occasionally when starting right when it actually starts. My friend said to check the tailpipe for excess carbon and there was, he says it's running rich and to have a diagnostic done on it. Has anyone had this problem? I plan on taking it in Friday after Thanksgiving but I read somewhere on this site that they won't hook it up to the diagnostic until 10,000, is this true? If it is running rich it may explain the less than expected gas milege.