The car has developed transmission issues, more specifically, shifting difficulty at higher speeds. When I'm driving at the speed of 65 mph and higher, I'm not able to shift gears. This has lasted for awhile now. I used to manage to shift by decelerating first and then applying the gas pedal again. Now this issue is worse. It would occasionally start shifting after driving for a while. While driving at lower speeds, I haven't experienced any problems. What could be wrong?
My guess is that the overdrive relay or solenoid has failed. If either of these parts fail, your Volvo will not shift into overdrive. This is a very common problem on Volvos such as yours. A trained professional, such as one from YourMechanic, will be able to diagnose your shifting issue firsthand to determine if this is indeed the cause.