I too have the 655 and it works great, even through a wall and upstairs from my two rokus. They have a great user forum for help, so I'd give that a try before buying another router.
Is your network ssid set to something other than the default? I've seen where two default ssid networks are close enough, and both have competing signals, where a device will switch one to another.
Also, check the firmware version in the dlink. One the forum they give their recommended upgrade procedure to follow, and there have been some buggy versions. Mine is the B version, so I'm speaking of what I know about that.
My method of troubleshooting a network issue is to set it up extremely simple.Turn off QOS and WMM, put it on the clearest channel, not Auto, turn off security, set it at G only, etc.
Another test is to acquire a long ethernet cable and see if its the wifi or some device conflicts. If a cable fixes the problems consider using a powerline ethernet adapter that utilizes your in wall power wiring to carry network signal to the device. This cheap solution fixed my family members issue when streaming netflix through several rooms.
"I might be moving to Montana soon..."
FZ