This is acutally pretty easy. Unlike the 3rd gen trucks, you could only get an HO with a six speed.
If it's a 2000, it doesn't have an HO. You could get the six speed, but the HO wasn't out yet.
If it's a 2002, and a six speed, it has the HO.
The tricky part is the 2001. There was a 2001, and a 2001. 5 (similar to the 2004 and 2004. 5) They made a few subtle changes. If it's a 2001, it won't have an HO. If it's a 2001. 5, and it has a six speed, it's got the HO. Now, how do you tell if it's a 2001, or a 2001. 5? I had a 2001. 5. There are a couple of ways to tell. Side moldings and brakes.
Side moldings (no moldings on Sport models

) In 2000, the side moldings went from the front tires all the way to the front of the rear tires. In 2001, they did away with the moldings on the bed. In 2001. 5, the little piece on the corner of the cab behind the doors was gone, and it was this way in 2002 as well.
Brakes. Simple. If it has 4 wheel discs, it's an 01. 5.
Hope this helps!
For what it's worth, I had a 2000 auto. It was a pig. I got my 2001. 5, and it was AWESOME

And it only got better with the EZ and injectors.
SOLER