2018 Silverado 3500HD with 6.0L gas motor. I notice in the morning when I start my truck, the idle stumbles moderately. As I back up out of the driveway, it stumbles as well as I pull way down the road. It immediately goes away once I get the RPM's up and is hardly noticable once warmed up and back in park. The truck has never had a "sewing machine" idle. It's always felt a bit "rough". The tach has a small bounce to it (tiny), but you can feel it in the seat.... Even when fully warmed up. Any ideas??