Post your DSL line stats using DMT v7.35 (»dmt.mhilfe.de/). We'll tell you if there's something wrong with your line.
If you haven't tried this yet, go into the router's config... Go to the SETUP tab Go to NETWORK SETTINGS on the left De-select Enable DNS Relay Save settings
That router you have is rock solid in my experience, with cable connections as least. Unless there's something terribly wrong with it, it should easily be able to handle a 5Meg DSL connection.