The cats that are displaced by the SLR headers are NOT the pre-cats, they are the PRIMARY cats. The 2000 model year had 4-cat (California-emissions) and 2-cat (Federal emissions) versions, and the 2-cat ones had the same upper/primary cats and were missing the secondary/lower cats.
There is a Frontier owner in PA that has them and has no problems. That is the only other owner that I know of that has him other than the one here that had problems with his.