What size tire (stock) and what gear ratio do you have?
The 3.73 w/30" tire package came stock with a 34 tooth gear. If you went to 33" tires you need either a 30 or 31 tooth.
Here are three sites that all give somewhat conflicting info:
<a target="_blank" href=http://www.raingler.com/jeepReference/speedoChart.html>http://www.raingler.com/jeepReference/speedoChart.html</a>
Above 32 tooth they do not have odd # til 39 ...hence any 33, 35, or 37 tooth references are bogus.
All the 231 speedo gears share the same part # 520676xx
The xx being the tooth count of the gear.
So a 31 tooth gear would be 52067631 etc.
If you had 30" tires and a 3.73 rear ..you will need a 30 or 31 tooth. I installed a 30 tooth and my odometer was within like 3% of stock. (54 miles on a 52 mile course) I may swap in the 31 and recheck it.
Oh..ya ..the Cherokee site has the detail on the install ..which is a snap.....except in my case. When I pulled the gear out the O ring swelled and I could not get it back in right. It would always bunch out the back (where you could not see) ..well eventually I ripped it and thank goodness the local engine/race car builder (which I was using his recently poured concrete lot to do this on) had O ring stock. This was naturally @ 4:30 when the dealer parts dept was closed.
So ...if you want to be safe (somehow I always run into the obscure anomolies) ..get a spare O ring when you order/pickup the gear.