Streaming Issues with new internet setup

Hi all, I'm new here but I'm hoping I can be specific as possible with my issues and I look forward to being a member of the community.

I recently moved into a new apartment and went with Xfinity internet by Comcast (the only internet offered). I bought the 75mbs package and have an Amazon Fire TV to stream various different programs.

My modem is a brand new Zoom DOCSIS 3.0 and my router is also a brand new TP-Link AC 1200. The router has two options and I'm currently using the 2.4ghz option (because my apartment is only 2 bedrooms).

Now, I left everything as-is on the router settings. I went through the install, renamed and secured my network with a password and that's it. I'm using dynamic IPs as per the option given when setting up the router. I have a laptop, a phone, and an Amazon Fire TV connected to the internet. That's all.

When I run a speedtest, I'm getting around 55mbs down (speedtest.net), but the issue I'm having is when I'm streaming on my Amazon Fire TV - specifically the WatchESPN app. The quality will go from great, to OK, to unwatchable, and then back to great again. It does this almost every 5 minutes making it extremely annoying. The odd thing is, I've streamed it a buddy's house who only pays for 24mbs internet and there are no problems whatsoever.

I'm not really sure what to do about this. Perhaps there are router settings that I'm unaware of that could resolve this issue? Maybe sending more bandwith to the Fire TV or perhaps opening a port?

If anyone has any suggestions it would be greatly apprecaited! Thank you again!