Slow upload speed through router

Hello,

I am having a problem with slow upload speeds through my router. I'm a comcast customer and am paying for 20Mbps download speeds and 4 Mbps upload speeds. Currently my download speeds are fine at roughly 18 to 20 Mbps, but I can only get around 500 Kbps on uploads.

I have a Docsis3.0 cable modem going into ooma (a voip phone device) which then goes into my Linksys WRT400N router. My computer is hard wired to the router. When I just go from the computer through the cable modem, or just go through the cable modem and ooma (without the router) my upload speeds are around 2.5 to 3Mbps which is fine. As soon as I add the router, the speeds drop to 500Kbps. I have also tried the cable modem directly to the router (without omma in the connection at all) and I still get only 500Kbps. So it seems that itdefintely has something to do with the router, but I can't quite figure out where to go from here.

By the way, I did just upgrade the firmware in the router to version 1.0.02.11 but that had no affect on the upload speed (either before or after the firmware upgrade).

Any insights would be appreciated. Thanks!

Edit (4/21/12): Just tested the speeds from another computer through my modem, ooma, router setup only it was done wirelessly through the router and I got upload speeds of roughly 3 Mbps and download speeds of 12Mbps. So this seems to confirm that my issue is with the hard wired computer connection to the router. Again, any insights would be greatly appreciated. Thanks.