There's sulfur in fuel additives; your engine isn't burning it completely and your catalytic converter is storing it and then releasing it as hydrogen sulfide when you add load to the engine and force more air through. That's what causes the rotten egg smell.

Try switching gas stations, or fuel grades; then try a thorough tune-up: replace the spark plugs, plug wires, fuel and air filters, and oxygen sensor, and clean the fuel injectors.

If that doesn't do it, replace your converter.

I'll check into what MB reccommends for the CLK 320 which is the engine in the Limited CF. Thanks and I'll try to run it but I'm in NY not TX so I'm cinda limited to streches of roads with police hiding around every turn.