I purchased a DIR-655 (A4) a few weeks ago, and was encountering a problem. I immediately upgraded to 1.35NA after I bought it. First, the actual problem: With WMM enabled, my internet speeds are very inconsistent. By that, I mean it will fluctuate between full ISP speed and less than half the speed. A few seconds at full, a few seconds at half or less, and so on. Well, when I disable WMM, with everything else the same, the internet speeds suddenly become consistently fast at full speed, but PC-to-PC (LAN-to-LAN) wireless transfers slow down considerably. So no matter what I do I get a negative result.
Thus, I figured I would try downgrading the firmware to 1.32NA, 1.33NA, or 1.34NA, as I read that it is not possible to downgrade directly to 1.2x. I thought I would simply troubleshoot the problem myself. Unfortunately, no matter which firmware I try, except 1.35NA, it gives me a paragraph explanation; something like "This file was either not intended for this router, or it is corrupt. Your router will not be programmed." It did allow a reflash of 1.35NA, though. I downloaded multiple firmwares directly from the D-Link ftp multiple times, using a different router, so the files should not be corrupt.
Is it simply not possible to downgrade once you flash 1.35NA? For the record, I also tried a few of the workarounds I found on the internet: (1) do a hard reset by holding in the reset button and cycling power for 30 secs. (2) I tried some firmware directly from the German FTP which was supposed to allow a downgrade, but still got the same error as above. (3) I also tried some Russian firmware and it didn't work either. I was using a hardwired connection to the router during all attempts to flash.
The router appears to be in fine working order except for the speed issue, but I find that issue unacceptable, which is why I am trying to downgrade firmware. If anyone has any ideas, I'd greatly appreciate them!