I have a WJ so i don't know much about ZJ's.
You can obtain a build sheet from this link, just replace the VIN with your VIN and you should be good to go.
It will tell you what it was delivered with.
https://www.jeep.com/webselfservice/...G858A83Y539160
Usually there is a tag on the diff that specifies the correct oil and the ratio that may be of assistance.
Jason