A week ago the overdrive f light began flashing, and at the same time when the vehicle shifts into 3rd it jerks and you can hear it. When it shifts down into 1st gear it also thumps a little. The check engine light is not on. Could this be the transmission going out or sensors? Otherwise teh car runs fine it does not slip or grind.
When the overdrive light flashes, it indicates the computer sees a fault in the transmission somewhere.
And it is my understanding that when the computer sees a fault in the transmission, it will increase line pressure thus making the shifts feel more firm. First find out why the overdrive light was flashing. That will point you in the right direction.