Firestick with Kodi will not stream live or 1080p

Guys, Gals, anyone!
I bought a firestick from firestick guru. I have the fastest Internet package from Comcast/Xfinity but I cannot stream anything live or anything 1080p. It gets stuck in “buffering” as if I’m using dial up.
Anyone have any ideas as to why I’m having this problem? I really want to watch UFC tonight but I know it’s not going to work.