The owner's manual says to drive moderately for the first 300 miles for the drivetrain.
The Diesel Supplement says to tow soon, or break-in will be delayed.
"A long break-in period is not required for the engine and
drivetrain (transmission and axle) in your vehicle.
Drive moderately during the first 300 miles (500 km).
After the initial 60 miles (100 km), speeds up to 50 or
55 mph (80 or 90 km/h) are desirable.
While cruising, brief full-throttle acceleration within the
limits of local traffic laws contributes to a good break-in.
Wide-open throttle acceleration in low gear can be detrimental
and should be avoided.
The engine oil installed in the engine at the factory is a
high-quality energy conserving type lubricant. Oil
changes should be consistent with anticipated climate
conditions under which vehicle operations will occur. For
the recommended viscosity and quality grades, refer to
“Maintenance Procedures” in “Maintaining Your Vehicle”. "
"The Cummins® turbocharged 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® turbocharged
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). "