Ah ok, that was on the Tahoe documents though, so I wasn't sure.That's for the NBS trucks (99-06), your 99 Tahoe would still have emerald green since GM continued it's full size SUV lineup 'til 99.
I'd get the 9779 Medium Gray color, looks pretty similar to the LT Slate Gray. I think the 7623 neutral color would be more suited for the 99/00 Esky/Denali.
I got the 857 medium gray. The 9779 med gray/pewter, looks pretty similar though