To be sure your ISP modem is in bridged mode, are you getting a 192.168 or a ##.##.###.### address on the 655 router under Status/Device Info/Wan section?
Any chance of testing a stand alone cable modem like a Motorola SB6120?
I'm getting a 192.168 address under the Wan section, and sorry, there's no chance of testing a stand alone cable modem.
I still say bypass the DIR-655 and see where we stand. But JMHO
I plugged my Ethernet cable directly into my modem's LAN port and did a speed test...
My download speed clocked in at 49.66Mb/s (lol wut) and my upload speed clocked in at 1Mb/s. I don't know how I got up to that speed though, I'm only paying for 24Mb/s (not complaining).

I'm going to try fiddling around with my router and see if I can get my Wi-Fi going faster, but I think I might just leave my computer plugged directly into the modem, lol.
EDIT:
Just did a couple more speed tests just to see if the previous result was a fluke:
Try #2 - 13.19Mb/s DL, 1Mb/s UL
Try #3 - 12.75Mb/s DL, 1Mb/s UL
Try #4 - 32.35Mb/s DL, 1.01Mb/s UL
Try #5 - 34.24Mb/s DL, 1Mb/s UL
So the results were really inconsistent, but the speed of the internet was a lot faster than it was with the router.