are there any new imac wifi connectivity fixes?

Have you reset the router, updated the firmare and done the same for your modem. Have you changed the DNS settings????

Have you changed the wifi channel on the router? It's worked for some.

Here's a catch-all of some things that have helped some people. It sounds like you've tried a few of them, but the links may offer other ideas - in no particular order:

• Check wifi security - if it's WEP change it to WPA or WPA2 (preferably, as it's more secure)
• Change the wifi channel on the router
• Create a new Network Location: http://support.apple.com/kb/HT5289
• Reboot the router

Also take a look at this link and the links within the article for other ideas. They mainly reference Lion, but still seem to be relevant to Mountain Lion:

http://osxdaily.com/2011/11/06/lion-wi-fi-problems-solution-mac/?utm_source=feed burner&utm_medium=feed&utm_campaign=Feed%3A+osxdaily+%28OS+X+Daily%29&utm_conte n t=FaceBook

...and this link:

http://osxdaily.com/2012/11/30/resolving-stubborn-wi-fi-connection-problems-in-m ac-os-x/