It was 2000 with a 34' Limited slide out. 2001 had the same model (and a special 70th Anniversary 30' model) and 2002 saw the 30' Slide unit added to the Classic model, along with the 34'.
I know that in 2001 in they made modifications to the slides within the model year. I saw one 2001 unit come into the Service Center and the modifications required them to pull all the cabinetry out on the slide side. They brought factory folks over to do the work. I think the owner said it was for water problems. I also know that they had a problem with the rollers that allow the slide to roll on the inside trailer floor. I'm not sure what year that was.
Personally I wouldn't be wanting one of the early slides prior to 2003. I'm not saying they were all bad but you can be sure the slide in my 2004 is a much better product that what rolled out in the earlier years.
'04 Classic 30' S.O.,'03 GMC Savana 2500,'14 Honda CTX 700