My 98 Dodge Durango doesn't go into overdrive sometimes what causes that

Well if your battery is old, 7 years (would survive a three second dead short, and spring back to life) Replace this one...next the black cable is connected to ground...undo and wirebrush that connection clean, use the garden hose to spray the crud away and re-assemble, also to the engine block with the fatty 1/0 battery cable...with a refresh of renewed power components that were not behaving will magically behave themselves again...invest $125.00 on an Interstate Battery (yes. the expensive ones) and reward yourself with excellent performance~