It wasn't clear that it was speed. I went back and read it. Plugging it into the router makes sense IF the router is fast enough. Check the speed of the router.
Do a speed test from other computers and see what the download speed and upload speed is.
You say they say it is fine. They may be checking from the node. They are probably checking from the modem. You can connect directly to the modem, but generally you have to connect to port one.
How can it be AC's fault if you have slow Internet speed? Take a laptop and connect it directly to the modem. Test your speed.
http://www.speedtest.net/
