I put the KKM on my 2000 XLT last night. It was a breeze to install (took about 20 minutes). I thought it would be loud, but I can't really hear any difference between the KKM and the stock set up. I like the fact that I can easily switch back to the stock set up if I needed to.
I have read some posts that state that the KKM may actually reduce performance during the hot summer months. I am not very mechanically inclined, and cannot verify or refute that claim, but it may be something for you to think about.
With that said, I am very happy with the KKM and I would recommend it.