Turning off the overdrive on a Ford F-150 is actually quite simple, and can be done quickly. First, locate the transmission selector switch near the gearshift lever. It will either have three or four positions: Park, Reverse, Neutral and Overdrive (if there are only three positions then Overdrive is incorporated into Drive). Move the selector to Drive without pushing in the Overdrive button. This will allow you to drive normally without using overdrive. To re-engage it later just push in the Overdrive button while in Drive and your truck will shift up into fourth gear automatically. If you ever need to turn off overdrive again just repeat this process; it's that easy!