From the 2020 manual under "Towing Information":
Do not tow a trailer at all during the first 500 miles (805 km) the new vehicle is driven. The engine, axle or other parts could be damaged.
Then, during the first 500 miles (805 km) that a trailer is towed, do not drive over 50 mph (80 km/h) and do not make starts at full throttle. This helps the engine and other parts of the vehicle wear in at the heavier loads.
From the manual under "Diesel Engine Break-In Recommendations"
The Cummins® Turbo Diesel engine does not require a break-in period due to its construction. Normal operation is allowed, providing the following recommendations are followed:
Warm up the engine before placing it under load.
Do not operate the engine at idle for prolonged periods.
Use the appropriate transmission gear to prevent engine lugging.
Observe vehicle oil pressure and temperature indicators.
Check the coolant and oil levels frequently.
Vary throttle position at highway speeds when carrying or towing significant weight.
NOTE:
Light duty operation such as light trailer towing or no load operation will extend the time before the engine is at full efficiency. Reduced fuel economy and power may be seen at this time. For additional vehicle break-in requirements, refer to “Trailer Towing” in “Starting And Operating” of the Owners Manual. Because of the construction of the Cummins® Turbo Diesel engine, engine run-in is enhanced by loaded operating conditions which allow the engine parts to achieve final finish and fit during the first 6,000 miles (10,000 km).