Q: Check Engine light on; transmission leak

The coolant temperature sensor is likely what caused your Check Engine light. Sometimes aftermarket manufacturers produce parts of a lesser quality than the OEM. However, this does not mean that all aftermarket manufacturers produce faulty parts. It is harder to go wrong with buying a KIA OEM part than an aftermarket due to the better warranty. I would recommend having the sensor replaced again with a higher quality part and see if the engine light goes away. As for the vibration at higher speeds, the transmission leak could be a contributing factor. Transmissions have even less tolerance for low fluid than an engine. If the transmission fluid is low its operation won’t be as good. I would recommend having your transmission fluid level checked and if it is low add some. If the vibration does not go away, internal transmission damage may have occurred.