differentials transfer boxes and axles use gl5 rated oil, like usually 80w 90 or stright 90. gearboxes with synchromesh like gl4 rated stuff. thats a fact. go check it out, i know toyota say gl4 or 5 but putting gl5 in will give you a really crap gearchange, it mite be fine when the box is brand new, but once the synchros are worn a little then they need a little help working , so putting gl4 in will give you a much much nicer gearchange.
you search the net guys. or even just read the pot of oil before you buy it, the oil i just put in my rav4 transfer box and rear diff said on it, for use in hypoid axles and differentials. no mention of gearbox, and thats a gl5.
and the stuff i put in my gearbox said clearly on it for use in modern 5 and 6 speed synchromesh gearboxes. oh what a suprise, that was a gl4!