iOS8 seems to have affected Wifi internet badly

Both my iPhone 5 and 5S have been flawlessly using our home wifi (Apple Extreme) until I updated to iOS8 yesterday. Now, even if I have a strong wifi connection, there's no or extremely slow internet connection. Occasionally, the wifi disconnects and I have to re-enter the password. The 5Ghz network can't be seen at all. I have tried resetting Network Settings, rebooted, and the problem will be solved but only for a while and then its back. Strangely, I have no problems with my iPad air which is also on iOS8. I spent a lot of time troubleshooting but till now can't solve this problem. Hope Apple fixes this quick.