Thank you for sharing these details with us.
Based on all the information you provided, I recommend you transferring a file from your computer to another (peer to peer) to check the adapter performance.
You can also get a troubleshooting guide from the Zip file at this location:
I have managed to identify the problem and have come up with the solution. It seems the problem was the Realtek LAN drivers I had... 8/15/2013 8.020.0815.2013... I updated to version 2/20/2014 7077 and that has solved the problem. However it ruined the WOL feature which I consider important. So after some chatting with old friend Google I found a much newer version at http://download.ecsusa.com/dlfileecs/driver/mb/lan/lan_4.7I_Realtek.zip which is stable and the WOL feature works better than before.