hi! i download my episodes just like you, from nyaa (1080p horriblesubs, though 720p works just fine for me also)! i’m not sure what is off in your case exactly, but i can give you some tips on how to make your gifs look higher quality:
i think that, off the top of my head, these are the main tips i can give you! if you have any questions about any of these processes, or if you try them out and still dont get the results you want you can contact me and i’ll try to find another way to help you;; good luck!!