I don't think I understand your post. If you are having typical overdrive problems it would be that the overdrive is failing to engage or shifting from 4th (overdrive) into 3rd (out of overdrive). This would explain your poor gas mileage. When the arrow is on overdrive will not engage causing the engine to rev higher than if the overdrive was allowed to engage. If this is the problem you are experiencing chances are it is the overdrive relay. Most people have good results with resoldering the circuit board of the overdrive relay. On your 740 the relay is located in the tray that is hidden by the ashtray. Remove the ashtray and then remove the ashtray holder. It is most easily accessed by then removing the cover from around the lighter opening and then removing the two screws that are revealed. This allows you to remove the little storage slot above the ashtray location. The overdrive relay is the one all the way to the right in the second row back- it stands up a little higher than the ones around it.

Randy