I have a 2002 duramax from CA. On three occassions over the past 8k miles it goes into an unusual mode for two to three days at a time. On cold start the WTS light stays on longer than usual and upon starting the engine runs very poorly with lots of smoke. After warm up it runs better (but not great) but the WTS comes on before starting, even in hot weather when at normal operating temp. The WTS has never been on after the engine starts. Within a couple of days it goes back to running great with no smoke or WTS when warm. Any ideas would be greatly appreciated.