Search "oil pumping phenomena." This will background one of the oil loss theories. I also have a post regarding the sudden loss of large quantities of oil, search again.

There are differences between the oil scraper rings and ring grooves from 99 to 00. There is a bulletin out there, which I have a copy of, dated 4/02. It addresses a change, to AFFECTED vehicles. However, I do not know what "affected" means, and I have no other documentation.
The fact is, there was a problem, and it's been corrected, or at least addressed. Don't expect Isuzu to own up to it though.

Interesting .pdfs: