Moody network connection, help

Hi!

A long shot but any ideas for helping me appreciated.

I have a MacBook Air, with both wireless and ethernet.

The network connection appears to be moody. Sometimes the connection screams. When wired I can get up to 10Mbps downstream through comcast, and roaming around on wireless generally seems to work fine.

But, when I sit at my desk, sometimes it's fine and sometimes not.

Periodically, the connection will slow to a crawl -- a gmail refresh might take 30 seconds, or it might not actually work at all. Load the espn homepage could take a minute or more. Crucially, accessing files on my NAS also becomes slow or impossible (it says lost connection with server)-- so I don't think it's an internet problem, nor the DNS problem I find when I search. Won't be able to access my network printer, either.

I had a MacBook pro before, never saw this problem. Have a PC sitting next to it, wired to the same switch: always works fine and fast during this problem.

Tried:
* Network diagnostics
* OpenDNS servers
* Turning off the wifi
* Connecting different wifi base
* Releasing and renewing IP
* Even rebooting doesn't seem to fix it!

The problem seems to come with 2 events:
* I show up with my laptop, open the screen to an already on session, and plug in the wired ethernet
* I plug in the wired ethernet to the USB where I was just wireless before
(pretty much the same thing)

Once it happens, I will have slow connectivity despite the fact wireless might have been working fine a minute ago

It fixes itself on a schedule I don't comprehend. Sometimes it will just start working, sometimes I will come back next day and it's working. Doesn't seem related to my reboot, disconnect wifi connection, unplug wired connection, replug wired connection

I'm at a loss! and I'm afraid a visit to the mac store will be useless, since my network isn't there. Want to throw this thing against the window sometimes!!

Any diagnostic suggestions welcomed. thanks for your help.