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Is the problem affecting just wireless, or can you reproduce it using a wired connection via the router? Have you tried changing the wireless channel, maybe there is local interference?
If you are using torrents, are you happy that the necessary ports on the router are open. Are you also sure that you aren't saturating your upload bandwidth. Many torrents may well see you as a new user as your IP may have changed after installing the router so that you may be at the bottom of the queue.
I've seen reference to the MTU settings sometimes being incommpatible with connections. I think the default is 1500, but sometimes that could be too high. Your manual may give ideas on alternative settings?