That's a cool program. I ran it and my signal strength was only 61%' which is surprising because the iMac is only about 2 feet from the wifi/modem. There are a lot of wifi signals in the apartment building, but im the only one on Channel 8.
I still however think its the imac and not the wifi connection. Ugh...
My imac 27" is new playing very slow on Internet , I have an unusual fault on my landline but the Broadband is testing ok, I have now put the Wi Fi on and everything is running fine..
Suggestion is that the WiFi function is a stronger and more capable with a possible line fault??
I hope that helps.