Stay with 99 or newer.
1997 was the TJ's official conception, but there were a few 96's.
DC messed with the TJ till they perfected it in the 99. The 97-98's were a YJ-TJ blend of electronic and mechanical controls.
You saw most of the major control changes finalized in the 2000. Including the inner electronic modules that are under the dash and wiring harnesses.
The 2001's was when DC started to mess with electronic doo-dads, to get them ready for the next big thing, the 2003 Rubicon lines.
2003 and on DC changed some of the inside trim and moved some of the computer modules around under the dash and wiring harnesses.
Most of these changes are not noticeable unless you have a pool of jeeps that you work on, we have a 89 YJ, a 97 TJ,2000,2001 and a 2003 that we work on as a group.When one person buys something we all gather to make drawing, and install it. The crux of having 7 jeepers working at a machine shop.
But personally I would go with a 4 banger for a strict city rig since gas is going up. (funny it never really falls either hummm)
Best yet since your keeping your YJ as a offroader only might I suggest a mini? I am looking at the prospect as well 28 MPG city...I hope my friends dont see me driving it.