I have a 2005 Silverado 1500 with the 5.3L engine with 62,000 miles. I had just left home yesterday and came to a stop at a stop light when I noticed the engine was idling rough. It was enough to make the tach fluctuate a little and I could feel it in the cab. As soon as I accelerated the roughness went away and everything seemed to be fine. When I came up to the next light the rough idle came back. At the third stop light in addition to the rough idle I could smell a strong sulfur catalytic converter smell and the check engine light started flashing. Once I was moving again the smell and roughness went away, but the light stayed on. Anyone had a similar experience? Any suggestions?