It looks like it has 8 lugs, so it's prob the HD version.
Good catch on the lug nuts. I think it’s too late at night and my tired old eyes mis-read the specs. I deleted that stupid post. So it seems they didn’t badge it as HD in 2000 but they did make a light duty and a heavy duty, with the later having an 8600 lb GVW.
Here’s a clarification of that GVW info:
“In 2000 there was no such thing as a 9200 lb GVWR 2500. Previously, you will see the 2500 rated as follows (there were no body labels to distinguish):
2500 (heavy duty) 8600 lbs GVWR (exactly this for all 2000 2500's (old body style Heavy Duty))
Also, the yr 2000 2500 (heavy duty) have 8 lug nuts on the wheels, the light duties have 6.
You could also get a new body style 2500 in 2000 (but not crew cab) that was either a light or heavy GVWR (7200 or 8600 lbs).
After the new HD line was introduced in 2001, the ratings are all screwed up. The 2001 2500HD is basically equivalent to the light GVWR option yr 2000 3500 (9200 lbs). The 2001 light duty 2500 is equivalent to the old heavy duty 2500.
Don't pay attention to the 1500, 2500, 3500 labels, just look at the GVWR sticker on the door. 8600 lbs and up is meant for serious hauling with a progressively stronger frames, axles and suspension components.“
(From GM truck owners forum)