What you might be encountering is confusion stemming from higher horsepower variants within the 2003 ISB engine family. These differences weren't denoted by "HO" but resulted from different fuel systems, turbochargers, and engine calibrations. To tell the difference between higher and lower powered versions, you'll need to look at:
* Engine ID Tag: This tag, usually located on the valve cover or engine block, will list the engine's serial number and potentially a code that indicates the horsepower rating. This is the most definitive way.
* Horsepower Rating: The horsepower will be stated in the vehicle's documentation (owner's manual, build sheet).
* Turbocharger: Higher horsepower versions typically had larger, more efficient turbochargers. This is visually identifiable but requires some familiarity with Cummins turbos.
* Fuel System Components: The injection pump and injectors are different between higher and lower horsepower engines. This requires a deeper mechanical inspection.
In short, there's no "HO" to look for. Focus on the engine ID tag and horsepower rating to determine the specific output of your 2003 5.9 Cummins.
