Hi, occasionally after driving for some time something happens to transmission. It.starts accelerating fine from a stop, switching to the 2nd gear and then to the 3rd and then engine's rpms start skyrocketing without any additional pressure on the gas pedal, and car continues moving at the speed of about 40 km/h no matter how high rpms are. The engine revs but the car moves at the speed of 40km/h. If I stop the car, switch off the engine, and let it be parked for a few hours, it starts driving normal again and the situation may not repeat itself. What is it? Transmission slippage or limp home mode? Thank you.