I am looking at fitting 4.11 diff gears in my stock 97 XH Ute. It's a 5 litre with a 4 speed auto. I have been told this will mess with way the auto shifts. Is it possible to just manually shift the box. I only need it to run down the drags for one meeting.

Dose the Auto change gears form the speed of the car or the revs of the engine?