How often does it happen? When the speed drops, link speed showing on your laptop and xbox is still normal or not? Wireless connection to C2 works OK? Sounds like the same problem here....

What's the WAN connection type? Actually, we don't have to manually input DNS server in most cases. Any problem with your internet connection?

PPPoE or Dynamic IP is selected as WAN connection type? The router won't lose the configure if you just reboot or restart it. When you turn it off, it will connect to internet automatically as well...

I thought you were trying to flash it with openwrt... As to TD-W8151N V3, there are only two firmware released. So you are trying to upgrade from 120530 to 140313?...

Did you read http://www.tp-link.in/support/rma/? There are details about how to get a replacement.

I would prefer to use Windows 7 as there is no driver for Windows 10 yet...