Peugeot 206 automatic gear problem please help

Hello, I started having the following problem after 8000 km in the vehicle I had a complete revision. My vehicle has no problem in a normal short distance, but when I travel around 20 km, the gears start to beat after 4500-5000 rpm. Tell me I connected it to the computer tonight, gave 2 error code al4 1-gearbox oil temperature: defective signal (intermittent) 2-No communication with BSI (intermittent) How can I get rid of this problem, what should I do?

By the way, my vehicle is 206 2003 model xt 70 hp automatic

isn't there a helper

Transmission oil cooler may malfunction. the oil may be overheating. Try to connect the computer and the transmission brain and see if it will connect. The transmission computer may be defective.

I went to the gearbox in the morning, the man connected it to the brain, he looked at the error code, the gearbox is in good condition, he said clean the throat throttle, he said, the voltage of the bidet battery was low, change the battery, he sent me. But my guess is that when the temperature of the vehicle rises, the gearbox gets hot, such a problem occurs when it overheats.

Didn't check the oil cooler?

I installed a thick type oil cooler. However, the temperature of the car cannot be cooled because the fan turns on at 98 degrees. What is your suggestion