5-90 the trans in my 87 XJ with 260000 miles on it is pretty much toast, fluid is burnt & it slips. A friend has a YJ that had an engine fire which I am picking up for parts for my son's YJ. I figured I could kill 2 birds with one stone as the trans is good in the burn job. I thought it was the AW4 but now i'll have to look at it again.
Simply compare the shape of the sump pans for the transmissions, and you'll see if they're the same or not (that's the standard method for identifying automatic transmissions.)
If the YJ isn't the AW4 - it probably isn't - try this:
1) Change your fluid, using something fairly cheap (
not Pennzoil, but some house brand that isn't made by them. Don't bother with synthetic yet.) Drop the sump pan, clean the pan and filter (the filter is just a wire strainer, it shouldn't want replacing.)
2) When you put in the new fluid, dump in a quart of Berryman's B-12 Chemtool with it.
3) Change your transmission fluid in two oil changes (~6,000 miles.) Clean your sump pan & filter again.
4) If you've noted an improvement (likely,) repeat the process. Carry on until you seem to "plateau" with the improvements, then return to normal service.
"Powerflushing" the AW4 isn't recommended, reports from the field are consistently negative.
Do not use ATF +3/+4 in the AW4 - the friction modifiers are all wrong and you'll have a Hell of a time getting rid of it all!
Clutch slip or chatter in automatics is most often a product of varnish buildup - since the fluid is also burned, varnish is almost a certainty. The B-12 will gradually break up the varnish and hold it in suspension, drain the fluid while it's hot when you change it (go for a drive immediately before.) Bear in mind that a "service change" like you're doing is only half of the fluid in the transmission, which is why you end up having to do it several times (the torque converter holds about another gallon by itself!)
However, most automatics prefer to be flushed "gradually" in this sort of manner, as it gives them time to adjust away from having all that crud in there. If the varnish is bad enough to affect operation, there's a lot of it, and you'll want to remove it gradually (unless you're going to tear the thing to bits and overhaul it entirely!)