Sure, it's possibly a defective unit.
Before reaching that conclusion, I'd do a hard reset to factory defaults and reapply firmware in a clean way, then reconfigure by hand.
When you phone in for an exchange, the Tech Support tech will have you do some of this again. If you've already invested too many hours, then just call in.
Otherwise, here's the process I'd do -- (download firmware from ftp://ftp.dlink.com/Gateway/dir655/Firmware/ before starting)
1. Using a pen, hold in the recessed Reset button on the back of the unit
2. While holding the button in, unplug power and then count slowly to 10 seconds
3. Still holding the button in, restore power and again count slowly to 10 seconds
4. Release the button, wait 60 seconds or so for the router to reboot
5. Without the button pressed, remove power, pause, restore power one extra time.
6. Install firmware, router will reboot as part of that process.
7. Without the button pressed, remove power, pause, restore power one extra time.
8. Now use the router, configuring it as you wish manually (don't restore a saved file)
The extra reboots may be unnecessary, but they are intended to clear any transient states or temporary variables caused by the process. Avoiding a saved configuration is an attempt to avoid any configuration corruption or confusion caused by changes of features and allowed/disallowed settings that have changed between versions.