Fast speed test, slow browsing/downloads/Netflix

Hello, I am currently paying for HD Preferred Xfinity Triple Play with advertised 20 mbps. Currently, my speed tests are running fine (pic below), but browsing, downloading, and Netflix are almost unbearably slow. When downloading files, I am only getting download speeds of 60-70 kb/s and my Netflix streaming is slow and laggy. As you can imagine, this is extremely frustrating.

http://gyazo.com/0f155d218fcee644c89611ca7b7aa522.png

Modem is a Motorola Surfboard SB6120.

http://gyazo.com/eafead38c87566a9088afb3e3dfef488.png

Error logs

http://gyazo.com/3c0cacf349a882960b20fd200fc86e4f.png

Speeds are the same whether my computer is directly connected to my modem, or through my Asus RT-N66U router either wirelessly or wired.

Here are my SharperProbe results:

http://gyazo.com/a6e00b1f2a7fb097d90c7493eab599d7.png

I have been a Comcast customer for many years and expect to get what I pay for, but am not receiving anywhere near the advertised speeds.

Edit: removed [img] tags and fixed links