The transfer case is like you were saying. There's 2 High, 4 High with open center diff, 4 High with locked center diff and 4 Low with locked center diff. Only one low ratio and you can only use it with the center diff locked.
i have one 4m40 mt in phils. its a great 4x4 except for being a diesel hog, it is one of the best. more parts available and no electronics. all mechanical.