It won't gear split on it's own other than shift into 4th (3rd over) at 43mph or whatever it's set at. You need to split manually which I have only tried a few times and with my setup it would be insanely hard to hit them all, not to mention I don't think it would shift fast enough to satisfy me. The shift into 4th at cruise is excellent and very crisp though, but I haven't tried under WOT. You can leave it on (OD engages automatically) or set to manual and do it yourself, which is what I have been doing. I didn't care for having two dimmer switches so I have a lighted painless wiring rocker/toggle switch in my console and love it. The dimmer switch may be faster for splitting though

Hope this helps.