Hello- I noticed a few times recently that the car would sort of seem to start losing power around 50mph and there would be a sound similar to wind buffeting or something and maybe a slight shuddering feel to the drive train. Stop and restart engine it would go away and then come again on another day. Yesterday it did it and when I went to slow down the brake pedal went all the way floor. I was able to pump it back up with a couple of strokes but the pedal still felt sort of soft. It did this several times until I made my destination. Today I drove home and it didn't do it, but the pedal still feels a tad mushy. Could there be a vacuum problem with the brakes that would affect the power of the car? It felt like it was only running on two cylinders or something. Sorry I can't explain it any better than this. Where should I start looking? The vacuum booster hose looks fine.

Thanks for any and all help!