Transmission down shifting

My transmission doesn,t always want to down

shift out of overdrive when climbing a hill

when driving down the hiway. I had new trans. filter and fluid put in but that didn,t fix the problem. My mechanic said the magnet was ok when he had the pan off. Thank you for a response.

Several years ago I had a mechanic that had this problem with Dodge Intrepid. Dealer replaced both the car and trans computer and eventually the computer, yet the problem continued. It turned out to be the ignition coil, the secondary winding was bad sending the wrong message to the computers.
Different brand of cars but it is an idea>

The Torque Convertor Clutch not releasing out of overdrive is typically caused by the failure of the Torqu Convertor Clutch Solonoid. It’s a small electrical solonoid in the transmission that switches hydraulic pressure to active / deactivate the clutch’s hydraulic circuit.

Over time, the solonoids begin to stick so that the clutch stays engaged. It’s an extremely common occurance on GM cars. About 10 or 15 years ago the solonoid caost about 40 - 45 dollars and took an hour or so to install.