Q: my car dont shift in high gears, but the transmission is good.

Hello. There are quite a few different parts that can cause this. It can be a transmission speed sensor, but a bad or defective throttle sensor can also cause this. If this started right after the throttle sensor was replaced, then you need to check and see if it is mounted and adjusted right. I typically use a computer scan tool to monitor the sensor reading, while pressing on the accelerator pedal to see if the sensor is reading correctly. If it is, then that is not the issue. From that point, I would need to check the output of the vehicle speed sensor, and check the transmission module for codes. That may show something different, such as a problem with a shift solenoid. It can also be caused by a voltage issue, or a blown fuse for the transmission supply voltage. My main concern would be if this occurred right after the throttle sensor was replaced. If this is something that you were looking to have checked, have a certified mechanic come to you to diagnose the issue of your car not shifting in high gears.