Buffering on new fire tv

I just installed a amazon fire TV with Alexa. I am having issue watching 4K and live tv , i keep getting buffering. I have a Vizio 4K smart tv and both the TV and fire TV show 4K shows with no issue. Only kodi has an issue.

What can I do ? Can I add a memory stick or sad card?

I just installed 17 and tarket as well.

HELP