Both of the engines available on the 2000 JGC use timing chains instead of timing belts. I have a 1995 with the same 4.0L Inline-6 that was used in 2000. It has 210k miles and timing chain hasn't needed replacement.
The 4.7L V8 (introduced in the 1999 model) actually has THREE timing chains. Apparently, there have been some high mileage failures on these engines, but the chain gets noticeably noisy prior to failure as a warning.