TowRig.com - Diesel Discussion and Tow Tech

I bought a 2000 2500 HD 4x4, 6.0 and on the window sticker it says "2500 HD"
I have read that HDs didn't start until 2001.
Whats the difference between the two....what makes an HD an HD ??

What is the productin date??????? At aprox. 07/00 General Motors, Ford, and Chrysler start producing the next model year vehicles.