I have a 2001 chevrolet blazer that has been having some misfire issues. When the engine is cold it takes 2 trys to get it started and then once it's running at 1000 RPM you can really feel the misfire. Once it warms up its starts with the turn on the key. I've ran 2 cans of gumout with no luck. When your driving it you cannot feel any misfires but as soon as you get into overdrive and it gets above 2000 RPMS the SES starts blinking and doesn't stop even though you cannot feel any kind of misfires. I have lost fuel mileage and the exaust fumes smell like rotten eggs. Any help is appreciated. Thanks!