No ideas, but I am kind of stymied by all of the wireless problems you have had over the years. I have never seen anyone with so many wireless glitches covering so many different pieces of equipment. There has to be some kind of interference or you're just really unlucky with flaky devices. Can you go all 5Ghz? If I remember you are using an older D-Link though.

How many wireless networks do you see under the Airport icon?

Does your modem have built in wireless?