Even with the theme clear skies, from fl200 and up, there is constant turbulence. So by time my plane reaches fl300, it has been pulling up and down so much its down nearly to stall speed, and then when it "steadies" out, it still pitches up 10 degrees, sets thrust full, pitches down 10 degress, sets thrust lower, which is very annoying.
Why is it doing this, and how can i stop it?
This is no slight, but have you been using the auto-pilot function in those planes that reach the flight levels you are talking about?
I find that when I do not use the auto-pilot, I am continually striving to keep the plane level and move up when necessary. Most if not all auto-pilot functions are pretty self-explanatory and can be found right on the cockpit or in the case of the Virtual Cockpit are very handy.
This will smooth out your flight level and keep you from stalling and/or losing control of your aircraft in flight.
Yeah unfortunately I have been using A/P, which is making the plane go up and down.