are my FPS being locked?

Your TV is probably only 60 HERTZ, not 60 FPS. You need to check your video card settings in your Nvidia Control Panel or Catalyst Panel, as well as your game settings to make sure your VSYNC is turned OFF to unlock your FPS so it will go above 60. As far as going below 60 FPS, that is your video card or CPU loading up on graphics, or your system caching data and slowing down.

All in all, it is not unusual. You may have to just tweak a few things to adjust for that, or realize your hardware may not be doing everything that you expect it to.