Is it caused by too much carbon deposit that the car shakes badly when it runs 40 in fourth gear?

Hello, running 40 in fourth gear should be caused by shaking. The speed of this gear should be about 60-75 kilometers. It is easy to produce carbon deposit when driving like this. After a long time, the car becomes more and more boring. It is recommended to drive at high speed occasionally to flush the carbon deposit. If my answer can help you, please set it as the best answer. Thank you very much. I wish you safe entry and exit and a pleasant journey.