Update...running now since yesterday afternoon with no wifi issues by implementing the "ping" workaround.
I tried the channel idea and it didn't work, but I selected channel 11, maybe I should kill the pings and go back an try channel 3, 2.5GHz.
One other thing...we were having terrible slowness issues with the imac when switching users. My wife's account in particular. She would switch and her apps took forever to start up...got the spinning wheel of death over and over again. Since I put the ping window in the background, we haven't experienced any of the previous problems with the mac responding very slow when switching users.
I wonder if there is some underlying network connectivity issue...