Hey Scotty, I have a 2002 Ford f150 4x4, 5.4L, 211k miles. When it's idling and at low rpm, it'll shake like hell. After getting to or above 1500 RPM, it stabilizes and drives pretty smooth. When I get to a light and fully stop, it starts shaking again. What could this be? I cleaned the throttle body, and changed the spark plugs recently to fix a misfire..