To clear up the EPA confusion
the designation Medium Heavy Duty vs Light Heavy Duty.
The first term (Light, Medium, or Heavy) refers to the life expectancy of the emission control systems- fuel systems, turbo, etc. The second term (L, M, or H) refers to the duty cycle or intended use. So, they are both actually heavy duty, but the PSD has a shorter life expectancy than the CTD. Look on the data tag of a NTC engine and you will see Heavy Heavy Duty, meaning a life expectancy of the emission system is something like a million miles. (I could be wrong on the numbers, though)
Daniel