Internet speed slowed down suddenly?

[Lainensis]

Recently my overall internet speed has taken a hit for some unknown reason and has slowed down noticeably.

I used to be able to load 1080p videos without ever needing to buffer or pause and now i have to wait 3-5 min to even watch a video in that quality.

As for online gaming my internet quality has taken a HUGE step down. Usual 3-5 bar games are unplayable. Even with friends i've played with before are having trouble staying connected or experiencing crippling lag and screen stutters.

For the usual internet use it hasnt changed too drastically but there are some noticeable problems.
Pages wont load even after numerous refreshes and my connection seems to have trouble loading more than 4 tabs at a time. Browsers crash during page load times.

For what its worth, i used to torrent frequently but never in excess, these problems started to show well into a time period where i haven't used torrents for months. My downloads were kept short and small without ever venturing to 10GB+ files. I've been experiencing this problem about 3 months or so and its been getting worse.

I have an Xfinity issued router due to my recent upgrade to their new system.

Why has my internet slowed down suddenly?