You are supposed to use a GL3, no sulfur content, eats the synchros and any other sintered [bronze, copper] materials. I run Redline MT90 in all of ours. Now we did have a 95 YJ with a 5 speed, that tranny got replaced and my son put Amsoil in it, that was 3 years ago and the friend he sold it to is still running it, he stops by every couple of days.
There was a mistake made in the manuals, started with ~98 and it took them a couple of years of replacing trannies under warranty because the dealers were putting GL5 in them. I think the correction came out in the FSM as an addendum a couple of years later.
I have also heard you can use Penzoil synchromesh but I'll just stick to the redline, to expensive to try something else just to save a buck or two a bottle.