I had at&t U-Verse installed yesterday. They disconnected my DSL 2-Wire modem at my Mac and installed a newer, larger 2-Wire modem at my TV. So, now I am forced to go wireless.
I encountered the same problem everyone here is talking about (full Airport signal strength but extremely slow internet connection) and discovered a fix.
You must change your Wireless Network Security on the MODEM, not in the Airport settings.
1. To get to the modem settings, open Safari and type 192.168.1.254 in the address bar.
2. Click on the Home Network icon at the top.
3. Click on the Wireless Settings tab at the top.
4. Under Wireless Security section, change Authentication to WPA2-PSK.
5. At the bottom, click Save.
At this point your modem settings will be changed to WPA2. HOWEVER, the modem page may fail to load and there is no telling that you have changed anything and you cannot access anything YET. So...
6. Go to the modem and disconnect the power for about 15 secs and reconnect to do a hard reset.
This modem will take a few minutes to come back on completely so be patient. When your TV signal comes back on your TV set, your wireless is ready to go. If your Airport signal is not active, you may need to re-select your modem from the Airport menu.
7. Open Safari and go to your favorite web pages. (Clear your cache first to get accurate downloads)
To perform a speed test, go to
http://www.speedtest.net and select the yellow pyramid closest to your location. Your download speed should be very close to your service speed. Mine is 3 mbps and the test came back with 2859 kbps. Right about on target. The speed I was getting while having the problem was about 150 kbps max, VERY slow!
Please post your result here if this solution worked or did not work for you.
Good luck!