as far as i know, with automatics anyway, there's a low setting so you have lots of torque (good for hills), and a high setting thats good for driving on stuff like ice, because you get less torque and therefore less wheel slippage. i think. thats what my auto-driving dad told me anyway.

also with big (and some small) 4x4's, they have a low and high ratio gearbox. i once drove a suzuki jimny (13 years old, not a recommended experience if you've got 3 back seat drivers in it and its your friend's mum's) that had a small lever that selected passive AWD, permanent AWD and low ratio AWD. might it be that? i'm guessing not, but its just a suggestion.