Unstable/Slow Internet Connection (iMac Late 2012, Win7)

Hello,

I've installed Windows 7 with Bootcamp on my iMac Late 2012 (2,9GHz variant), but I keep getting internet issues. Although the computer is connected to the router and has stable and fast (50k mbit/s down, 10k mbit/s up) internet on OS X, the internet speed on windows keeps dropping down to 0-200kbits download and 0-10kbit/s upload every few minutes. Moreover the connection breaks down completely irragularly and is up on highspeed a few seconds later again or keeps being broken for an hour. All in all its extremely unstable and inconsistent and makes it almost impossible to watch videos on YouTube, play games online or use Skype, especially not at the same time.

- The dsl connection to the router works perfectly fine, without having any problems or errors, no other device in the network has issues

- No other network is on the same WLAN channel, which could potentially slow down the connection

- 802.11n is used

- Windows 7 is completely updated (SP1)

- BootCamp drivers 5.1.5621 (recommended for my computer) are installed and up to date

- Router: FRITZ!Box 7362 SL (UI)

- I am using Windows 7 Home Premium 64-Bit and OS X Mavericks 10.9

I'm looking forward to your replies and hope, that anyone can help me out with this problem.

Greetings from Germany. -Sören