Do a search, there are several threads about the correct fluid for the AX-15, AX-5 and XFER Case.
GL-5 is a misprint, DO NOT use it, GL-5 fluids contain additives that can become corrosive to the synchros if it gets warm enough.
GL-3 Manual Transmission Fluid is the correct fluid to use. The Syncrhos require some sort of friction modifier, so regular gear oil (NO FRICTION MODIFIER) could cause shifting problems. Besides, most gear oil is GL-4 or GL-5.
People have used Redline MTL and MT90 (thicker version of MTL) which is technically a GL-4 fluid, but it advertises that its additive won't become corrosive to the synchros until triple the temps of regular GL-4 and GL-5 fluids.
ATF for the XFER case. ATF+4 is synthetic ATF, ATF+4 has now been licensed and they now sell it at reduced prices at Walmart and other stores. I have no Idea how well it work, I don't know if anyone has tried it, but I don't think the XFER case are to finicky as to which ATF you use, as long as its ATF. Some people are big endorsers of Synthetic ATF, so maybe ATF+4 might be a cheaper synthetic ATF.