overdrive
I turn mine off towing the boat on short runs to the lake or on the highway through the hills, but leave it on if the highway is level and the trans is not downshifting on its own. When not towing, it stays on unless in the mountains.
I also turn it off if going through town where there's red lights/stop signs. My truck kicks into OD at 40mph and usually as soon as I hit 40 it's time to stop. So I figure it's better to keep it out of OD so it isn't shiftin as much.


