prettyjay

am having a problem with my transmission for about a week now. I have a 1993 SC 300 with 134,000 miles and everytime I get on the freeway, which is everyday to go to work, and I get up around 50-60 mph the transmission shifts as if I just pressed the overdrive switch and the RPM will go from about 2500 up to 4000 and the transmission will stay in that the condition until the car is turned off. I have no problem accelerating however when I do the RPM goes into the 5000-6000 range.

I took it to get a transmission filter change and flush, and the tech said that the transmission was good. Next step was I had the Throttle Position Sensor changed and the cable to the transmission adjusted that didnt help either. It just seems like when the transmission changes like that it will not go back to normal( meaning when the overdrive is on) unless I turn the car off and let it sit for a while. Also when it switches like that, I tried pressing the overdrive switch on and off and it is like the button does nothing at all to return the car back to the normal state( over drive on).

Please someone help!!!!!