Well after suffering over two weeks of constant wireless restarts and really bad lag on the Xbox 360 and WoW, this morning I finally got this blasted DIR-655 working like it should be. What was the fix, you ask? Switching from WEP to WPA-Personal - yep, no other changes made this morning. I had tried a good deal of the suggestions here (disable DNS forwarding, disable QoS, blah, blah, blah....) and though these seemed to slightly reduce the number of wireless restarts, they still continued.
I know that WEP is not as secure, but it seems like it is a very basic function of the router (and has worked fine for me in the past on other D-Link equipment). Looks like the developers are too concerned with the hot new features that they let some of the basics slide.