I had this same problem and the fix was easy. Our thermostat was stuck open and the car wasn't getting up to temperature. Until the car gets up to temperature, it won't shift into overdrive. If your temperature gauge only moves when you are in stop ang go traffic, change the thermostat and you should be good.
...ift correctly. This can be caused by the throttle position sensor being out of adjustment or a shift solenoid needing to be replaced. Typically the transmission does not need to be completely overhauled.