|If you haven't yet contacted your ISP and discussed the modem they've supplied you with, you should. At least, I'd start there. If they find nothing wrong then you may need to replace the router.|
The only thing I can think of at this time is to ensure you have the most recent firmware installed in the router.
Just FYI, there may be nothing wrong with any of the equipment in your home. If it slows down again, try different servers and see if that makes a difference. It could be just the server you're connected to is slowing down, not you. What are you doing when it slows down?
It matters not how straight the gate,
How charged with punishments the scroll,
I am the master of my fate;
I am the captain of my soul.