I have a well worn 1984 CJ with 4 speed manual transmission.
I would assume that a 1984 with auto would be ready for a rebuild. check it out as it may be a two speed auto trans, not a 3 speed, like you, I have never been around older models jeeps with auto trans.
about all you can do is pull the trans dipstick and look at the fluid, is it dark and dirty, does it have the proper level of fluid.
take the vehicle for a drive and be sure it shifts properly, drive it long enough for the transmission oil to get warm, that is when you need to run your test,
others will chime in here, but I would think it would take at least a 30 min drive for the trans oil to get warm.
shift in each gear and be sure it pulls fine also check the 4 wheel drive transfer case and be sure it pulls, may need to find some loose gravel to check that, for you to see if the front wheels pull.
in the woods going slow, I like the auto, as you do not have to always pump the clutch to go slow.
auto trans: some like them, some don't, guess that is why there are so many more manuals.
I would think a auto trans jeep (older model) would be less desirable than a manual, but that is just me.