There is no such thing as a 60fps gif file, unfortunately. Most 60fps "gifs" are actually mp4 files. GIF files don't use a framerate internally, they use a frame delay, which is how long to display each frame before moving on to the next. This delay can only be specified in 10ms increments, and 60FPS = ~16ms delay. If you are trying to make a smooth GIF file, I recommend no higher than 50fps.