Q: Transmission thinks it's in 5th gear. But resets when you turn it off and turn it back on

Hello. If your transmission is having trouble identifying gears, then there is likely an issue with one of the sensors or components. It may be possible that the input or output speed sensors, or one of the shift solenoids is going bad and is causing the issue. It may also be possible that the issue is electronic in nature, if the problem goes away after you restart the vehicle.

Perhaps there is a problem with a wire, or even one of the computers. Also keep in mind that transmissions operate using hydraulic pressure, and can have major issues if one of the pressure components, such as a valve body or pump go bad. I would start by checking the transmission fluid level to make sure that it is at the proper level and not excessively dirty, and then go from there. As transmission issues can sometimes be difficult to diagnose especially with high-end vehicles, I would recommend taking the vehicle to a shop for a better assessment, if you are unsure.