Router Slowing Speed of Cable Modem

Hello all,

I'm using a SB5101 with a Linksys WRT54G w/DD-WRT. When I do a speed test with speakeasy.net I get 35Mbps without the router and 25Mbps with the router. I'm doing the test with a wired PC. (I disabled wireless.) I changed all patch cables but it didn't help. Can someone tell me why this would be?

Thanks,