What designates if you have the Cummins HO motor in your truck?? I have a 2005 heavy duty with the 325 horse and 610 ft. pounds of torque straight from the factory, but no where on my engine does it say HO.

 

Iv got the same truck and I believe there is a sticker on the left side of the engine that states the HO
The earlier versions were rated slightly less.
Someone with more knowledge than me should be able to give you more info.

 

it's the only available motor for 2005. all of the 05's were the 325/610 motor