shaking or vibrating at low speeds almost flat ground(about 20 mph) also shaking while sitting at stop light.
You should have a mechanic look at that.
When you talk to them, explain more fully. What you’ve posted here isn’t going to help much.
Just a wild guess but a rough idle will do that. A rough running engine tends to smooth out at higher RPMs. A bad idle air control valve will cause that, as will poor compression in one or more cylinders. Has the check engine light come on? A good mechanic with hands on the vehicle can diagnose whatever’s wrong.