Ah, so.
You used the 'Diags' system to re-install the older, 'Main' firmware.
That is good to know and good to have the link for people searching for the answer.
And that is another point in favor of recommending that everyone install the "Rescue Pack".
= = = =
I do not mean what channel(s).
I mean protection mode: WEP, WAP, WAP2 ...
Ref:
http://www.wi-fi.org/discover-wi-fi/security
Not all firmwares, all models, have been able to use all modes.
And I am thinking that might be effecting the results that you see.
Although I will go with your theory - too many, very strong, conflicting AP devices in your immediate area.
Try setting up your AP to use one of the band-edge channels, just leaving it on 6 is what everyone else does.
And a short article on the gap between what (self described) "tech savy" people claim to be aware of and what they actually do in practice:
http://www.wi-fi.org/news-events/new...-know-and-what