I've been using the Dir-655 for 2 or 3 years with my old Xbox 360 and an external G wireless adapter. Everything was working perfectly until I got the dreaded Red Rings Of Death the other day. I replaced the Xbox with a new Slim version with built in N capable network adapter.
After more than 10 hours of trying a variety of "fixes" I found from MS and in this forum, I am still at square 1. Arrgh! I read the sticky Furry always refers us to. No help I'm afraid.
Hardware Version : A3
Firmware Version : 1.32NA (this is listed as Live compatible by Microsoft)
802.11 Mode : Tried N only, G only and mixed 802.11n and 802.11g
Enable Auto Channel Scan : Checked
Transmission Rate : Best (automatic)
Channel Width : Auto 20/40
Visibility Status : Visible
Security Mode : WPA-Personal Also tried WEP
WPA Mode : Auto (WPA or WPA2) Also tried WEP
Cipher Type : TKOP and AES
I tried assigning an IP manually from the Xbox. But, no matter what I do, the router will not accept it. It is especially frustrating that the Xbox is visible to the unit. It simply will not assign an IP to it under any circumstance.
If you read the sales hype promoting the Dir-655, you will see a lot of nonsense about it being great for gaming. Given that, you'd think a simple solution would have been found and posted for this issue by now. Surely, end users shouldn't be trying 100 different possible "fixes", none of which work, at this late stage of the firmware upgrades. If I sound a tad fed up, it's because I am. After the expense of the new Xbox, it appears I now have to junk my router too.

They call me 'Gears'
Here is the status screen taken when it was in mixed mode. Changing it to 'G Only' didn't make any difference:
