There were three transmissions used behind the 4.0 in 1989...
Automatics were AW4 Aisin-Warner four-speeds (three + overdrive.)
Early 1989's used the Peugeot BA-10/5 five-speed (four + overdrive)
Later 1989 (AUG1989 and later, I think) got the Aisin AX-15 five-speed (four + overdrive.)
Easy way to tell? Get under the thing and check the transmission case - if it has a longwise split, it's the Peugeot. The Aisin will have an intermedate plate, as well as a "forward gear case" and a "rear adapter case" - it will look like two sleeves bolted to an intermediate plate in the middle, and parting lines will be crosswise.
I think there are pix of both boxes online - you might want to start looking at Jeepin.com, I think, for tranny pix (unless someone here can give a better source...)
5-90