Very Unstable Internet Connection

And, you don't have the same problem when connected by ethernet, right?

Please attach a screen shot of the Networks page (don't collapse the Radar, Connection or Signal History) of the Xirrus Wi-Fi Inspector. If you need help with a screen shot see TSG Posting a Screenshot. FWIW to take screen shots with Windows 8 or 7 or Vista I prefer to use the built-in Snipping Tool.