If you find your 802.11n Wi-Fi network is unexpectedly slow but a strong signal is produced, this Network World tips article suggests you should look at the type of password you are using.
“While this is not exactly a new discovery, Apple chose to highlight it in a detailed support article just posted Thursday. The article explains that, if you use a WEP or WPA (TKIP) password, the maximum transfer rate will be 54 Mbps, even on a otherwise properly configured 802.11n network. As noted here, the maximum possible speed with an 802.11n network is about 300 Mbps, although realistically you are more likely to get in the range of 130 Mbps.
“To get the maximum possible speed, choose a WPA2 Personal password. If you have an AirPort Base Station, your only password choices for 802.11n networks are WPA/WPA2 Personal and WPA2 Personal. The latter option is the recommended one. If you have more than one device connected to the router, the former option can still result in slower speeds.”