Just wanted to drop this out there as it helped me and is commonly cited in these halls as a possible remedy.
I have Charter cable ISP and currently get 30mbps dl speed. Last month we have had major issues with Charter equipment along our rural road, but now fixed. So, yesterday when the speed dropped to single digits I immediately called Charter. They said everything looked fine, from their end to my modem. I pulled the 655 out of service, connected desktop to Arris modem and speeds were holding at 30. Router back in, speeds down. Restored my config file to router, no change. Put another router in place and speeds were great.
So then the advice to reset to factory and manually reconfigure came to mind and all is now well. I was thinking that this old router was going to need replaced.
I think that many folks dread this step because you have to know all of your existing settings to be able to easily reconfigure. Imagine if there was an option in the router to "save to file" any altered from default settings, so it could be printed out. Hey Dlink, maybe you could have someone look into that.
Good luck to all.