I noticed my D-Link Wireless N+300 Mbps Extreme-N Gigabit Router (DIR-655) seemed to drop connections whenever someone was streaming a video. Then I remembered a similar problem with the old router I replaced this with and went looking through the settings.
Under ADVANCED –> FIREWALL SETTINGS –> “Enable SPI:”, you’ll want it UNCHECKED.
This seemed to solve any sort of network slow down or dropped connections. Also, you’ll want to disable QOS if you have it on.