Thanks to www23, I've been able to downgrade to 1.21 firmware, and my 655 is once again behaving well. With 1.32NA and 1.33NA, the wireless signal would blink out multiple times a day no matter how little I changed the settings from the factory values. After downgrading to 1.21 and using the exact same preferred settings that I had used with 1.32NA and 1.33NA, the wireless radio has been rock-solid all day. Its so nice to have a router that actually works reliably.
EDIT: A couple of people have asked me how to perform the downgrade. Its covered in the link below over a series of posts:
http://forums.dlink.com/index.php?topic=10668.0
I'll summarize here.
NOTE: I have only tried this with an A4 router. I saw one report of someone getting it to work with an A3 router, but that's all I've seen on that. IF YOUR ROUTER DIES, ITS NOT MY FAULT.
1) Download the "dir655_Downgrade.rar" file from the following page:
http://www.dslreports.com/forum/r23684438-DIR655-Firmware-Downgrade-13xNA-13xRU-IPTV-Work
2) Decompress the rar archive. (i.e., make sure that you have software on your computer to decompress a RAR archive.)
3) Go to the dlink ftp site to get whatever firmware you want to use:
ftp://ftp.dlink.com/Gateway/dir655/Firmware/
4) Reset your router to factory defaults using the button on the back of the router. The button has to be held down for a full 10 seconds. (Doing the reset is probably not necessary, but I always reset to factory defaults before installing a firmware.)
5) Install the RU firmware on your router. Let it go through the entire install process.
6) Log back into the router and install the firmware that you want to use (1.21 or whatever).
7) Setup the router to your liking. I do not recommend trying to upload any saved settings from firmwares newer than what you have just installed.