A few additives do make the Cummins a little quieter.
Usually, a bad injector will cause a rough idle.
A few of us figure if we can't get smoke out the tail pipe, something must be wrong with the injectors!!!
An injector can be plugger or partially plugged. Or leaking, or the 'pop-off' spec is out.
If you have spent a lot of time with it loafing around town, it may need a road trip. Best with a trailer. These trucks are made to pull.
I remember a few decades ago when I was helping dad on the farm. We would do light duty work with the tractors all summer. Then when it was time to plow, the first day we had to run a gear lower than normal. Second day, gear it up and go hard. They even started better after a good pull.