Good morning and thank you for posting on the Final Fantasy XIV Technical Support Forums.

The game is only like this in windowed, correct? Does this same issue occur in borderless fullscreen? Does reducing some of the settings or resolution affect anything?

There is an option in the settings menu that will limit the frame rate when not focused. Make sure this was not accidentally selected at one point.

We hope we can be of assistance in helping you enjoy the exciting world of Final Fantasy XIV!