to shift from 4high to 4low and visa versa you have to come to a complete stop and put the tranny in neutral.

When you first put it in 4high you must be completely stopped but after that as long as the "wheel lock" light is on you can shift between 2wd and 4high while driving at any speed, just move the shifter.

1989 Montero 4dr V6 3.0l