Check gearbox when cool as follows - easier with 2 people:
1 person under vehicle - just loosen (don't remove) filler plug. This is on side of G/box sump opposite end to drain (if I remember correctly)
1 person in car - start engine and run gear selector through all positions (make sure they keep their foot on brake at all times!!)
Put selector back into park and then remove filler plug. Fill through hole until a 2mm bead runs out.
Replace filler plug and tighten - stop engine, all done.
You should use ATF to Dexron 111.
Hope that helps.