time capsule internet speed is slow

Replaced my LinkSys WRT610N Wi-Fi router with new Apple 2TB Time capsule, only to find that the internet is under barably slow. To validate that the problem is with the Time Capsule I reconnected the ADSL2+ modem to the LinkSys WRT610N router and found that the internet speed has returned to normal. Any chance that that anyone has experienced a similar problem and have managed to resolve it? I also find some pages more responsive that others, which is something I find odd.

Note: I have already used iStumble to identify other Wi-Fi devices and changed the Time Capsule to make sure that it only works on a channel which is not used by other Wi-Fi routers in the area. The computer I am using to set up and connect to the router is the very latest MacBook Air.