idling a modern diesel is a bad idea (builds soot really fast). If you drive the 3.0l around town it will regen more often but the 3.0l is less sensitive to non-highway/light load than the 6.6l is. A normal regen takes about 10 min on the highway. If you drive at highway speeds or loaded it will likely regen based on mileage or time and not soot level. One of 3 things will trigger a normal regen on a GM. Time, miles since last regen or soot level. Just an FYI but the GM diesels will stop a normal regen when the engine is idled in park and restart when in drive and moving again.