History:
I have the dir-655 V: a2 (love them) bought over 8 of them for friends and family who needed routers 1 time setup never have to touch them again.
I have had mine over 3 years.
I am not sure exactly what the trigger for this was but on 6/2 I could no longer keep a good 802.11n connection on my laptop.
I did thorough troubleshooting regarding the laptop network but to no avail.
So I check the router and notice that none of my n devices are connecting via the n protocol. All are connecting via the g protocol.
Rebooted the router for the first time in ages and it took a while for the auto negotiate for uplink was taking a while and when finished my network speeds went to 2mb Down/50kbps up. My normal Mediacomm cable connection is 12mb/1mb
Bypassing the router I got correct speeds from my ISP.
Reconnected router, back to 2/.05.
Turned off all other network devices (two 802.11n phones, 802.11n laptop, 1 802.11g printer , 802.11g Wii, and 2 of my wired desktops. )
Rebooted again, no change.
Found out the button in the router to check for updated firmware was not giving correct results.
Updated firmware from 1.21 to 1.35NA
Reloaded previous config file, same issue, 2down/.05 up
Reset factory defaults, no change.
I had an issue about a year ago when I setup some port forwarding on the router and with the port forwarding on it was doing the same thing and through very little help from dlink support figure out that by manually setting the wan speed from auto negotiate to 100mb it fixed that issue.
After resetting factory defaults, changed wan port to 100mb , still no change (and of course as everyone knows I rebooted the router after every change since you must

)
So while troubleshooting and handling router I noticed it was very hot, even though it’s in a well ventilated area. So I thought maybe I popped a capacitor and it was just dead. No big deal such is life I ordered a new one.
But wait… Coincidences of coincidences I am helping a friend with his network bridge at his office the next day and in his closet is a dir-655 sitting in a closet not being used.
He was having network issues and his ISP came out and said his 655 was the problem, he went and got a new router and problem solved.(he was not told what was wrong and has no clue why it was the router).
So I snag it from him, take it home to mess with and everything looks fine on it so I hook it up to my cable modem and OMG it does the same exact thing.
2mb down/.5 up
Updated firmware because he was also on 1.21 to the 1.35NA
Reset factory defaults. No change
Changed wan port to 100mb, no change
So I am thinking there is too much of a coincidence on this. So I do more digging and not sure where I saw it but someone pointed me to the QOS engine uplink speed.
Unchecked the Automatic uplink speed, set manual uplink to 1024kbps
Changed connection type to cable or other broadband network
Rebooted and wow it works on my friend’s router.
So I go to mine changed it on there and fixed it too.
SO… in short there is a firmware issue or something causing the auto negotiate on the QOS engine uplink speed to not work properly.
Hope it saves someone else some money since I got a new router coming in the mail that I don’t need any more.