For the past few months my iMac's wifi has been dropping or running so slow it won't load even simple webpages. If I turn off the wifi and reconnect it will speed up but only for a minute or two and go back to running incredibly slow. My macbook pro will run perfectly in the same room. I've tried all the simple things (turning off, restarting everything, turning off all other wifi devices). I am using an older airport express (g). Maybe thinking that is the problem since it seemed to happen when I updated my iMac to 10.8.2