The important thing is it goes back up to 59.
Offline up a P51D and sit on the runway. Hold down on the trigger firing off all of your rounds. You may see your FPS drop considerably. But, if you only tap bursts, it stays steady. This may be more the way video processing is performed in this specific game than anything else. You have changed your screen by moving a graphic rendered overlay object. Essentially a window within a window. This may be why Hitech warned us he won't give us rear view mirrors because some players would have an advantage while many would see reduced FPS and I suspect stuttering.
You can try updating your drivers or reducing the video bells and whistles you have checked in the advanced graphics. You may even have too many services running before you launch the game. If you use TrackIR, make sure it's application GUI is minimized before you start the game or, if you minimize the game to adjust your TrackIR profile a lot, make sure you minimize before going back into the game. Personally I'm waiting until after Hitech introduces the use of "Shader" with the new terrain engine to worry about graphics. You are describing pretty standard features of this game.
In the Technical Support forum you could open a request to help you get the most from your current computer OS and hardware.
