Toyota has used the AX15 for years. In addition to authoring the Jeep Owner's Bible, I wrote the Toyota Truck & Land Cruiser Owner's Bible. Jeep and Toyota generously supplied period OEM books for my Bentley Publishers' ventures...
I just pulled the '93 Toyota T100 shop manual off the shelf, and guess what? Toyota recommends API GL-4 or GL-5 and a 75W-90 rating for the transmission lubricant. Given that Toyota has produced far more trucks with Aisin transmissions than Jeep, let's consider this insight useful. As for which GL-4 or GL-5 75W-90 oil to use, I believe this comes down to lubricity.
Many years ago, when I wrote the "Holy Moses!" tech Q&A column for OFF-ROAD Magazine, I became enchanted with all oils synthetic. This held true for engine oils and gear lubes, and my Jeep Owner's Bible, from first to third editions, promotes Mobil 1 engine oil...At the same time that I became infatuated with Mobil 1 engine oil, I recommended Mobil gear lube to the readership of the magazine. Lo and behold, I received a nice letter, tactful and diplomatic, from a Toyota truck owner. (This was around 1988-89.) He shared that when trying Mobil synthetic gear lube in his transmission, the unit developed clash on shifting.
I deduced that this was from insufficient braking action of the brass blocking rings, and I immediately sided with him, noting that the recommended Toyota lube, non-synthetic in those days, worked better in his gearbox. The Mobil gear lube had too much lubricity, which simply would not allow the rings to brake properly against the gear hubs during synchronization. (The rings slipped on the hub rather than grabbing it.) He changed back to the OEM lube and did not have a problem thereafter...I stopped proselytizing synthetic gear lube as a "universal good thing"—unless recommended for a specific gearbox or axle application.
So, that said, I recommend either the original Mopar AX5/AX15 Lubricant (if it can be found in NOS form) or Toyota's recommended API GL-4 or GL-5 in 75W-90—as a non-synthetic choice. (In 1993, Toyota did not use synthetic gear lube as a factory or dealership service fill.)
Redline may have a specific lube that works well with the AX5 or AX15, so I defer to Redline's experience here. Ask Redline to be sure. There is so much buzz about AX transmission lubes that Redline should have this down by now. Also, Amsoil has a tech line, you might compare viewpoints.
When a Redline or Amsoil official recommendation comes forward and gets tested by someone in this forum community, please report back. Maybe we can put the "AX oil" thing to bed...Moses