radiazone,
you can use your 4low on a pave road provided you don't engage your front hubs. this would multiple your torque increasing your pulling power especially when going uphill. I do this when going thru deep flooded streets like in the sampaloc area. This way I don't need to rev the engine (prevent splashes to the engine) that much. let me add that you can use your 4hi and 4low on paved roads provided you drive straight with minimal turns.