When is the best time to use over drive, or OD off? On the highway I imagine it should be in OD, but not in town? When I leave town to go home, I drive about 70km/hr up and down hills and around sharp turns...should OD be off then or on? And more importantly, do you have to be at a stop to push the button for OD or can it be on the fly?
Thanks for any input, I don't have my manual for my 4.7 D.

The OD is shift on the fly. When you are going up hills, stop and go traffic, towing, and cruse at about 35 mph then the overdrive should be switched off.

Other than that run with it engaged for gas mileage. It is better to install a trany cooler if not equipped. This will make sure the trans is running cooler and increase longevity.