I'd say LX & LT are just Toyota USA specs. They're not API or SAE as far as I'm aware. The same oil is used in other Toyota vehicles with plate type LSD, so I'd say LX has friction modifier in it & LT doesn't.
The NZ/AU
service schedule makes no mention of LX or LT. Just use a GL5 designed for an LSD & you'll be right.
*EDIT*
Found some basic spec on "TOYOTA GENUINE DIFFERENTIAL GEAR OIL LT 75W-85"
Part number 08885-02506
76 cSt @ 40°c
11.5 cSt @ 100°c
They're a Torsen LSD so don't require friction modifiers.