Slow internet

I've been having this problem with my internet for a few months now. At first it was rare, happening once every other week or so but usually on evenings so I figured it was just neighborhood congestion. Then it started happening more, a few days in a row but still during evenings. Lately it's been happening constantly, and I find that when I'm using twitch.tv to watch live streams then my internet speeds will drop across the board. The internet works fine when plugged directly into the modem and I've replaced the router last week with an Asus RT-N66U but the problem still persists. Hoping to see if anyone can solve this before I have to call over a tech. 

Here are the readings from my modem:

http://imgur.com/a/BNKlO

Here are the speedtest results. 

Not using twitch.tv: 

http://www.speedtest.net/my-result/3724881111
http://www.speedtest.net/my-result/3724883406
http://www.speedtest.net/my-result/3724885510

Using twitch or a half hour after using twitch.tv:

http://www.speedtest.net/my-result/3724888004
http://www.speedtest.net/my-result/3724893835
http://www.speedtest.net/my-result/3724895631