Internet speed/throughput

Hello all,

I upgraded from preferred to premier internet service yesterday.I am not getting the full 50mbps (or at least close to) advertised speed.  Am only getting 17mbps with desktop connected directly to ethernet port on router. But if I connect the desktop directly to sb6141 cable modem ethernet port, I get 60mbps speed. is there a router configuration that i missed ?. any help or suggestion would be greatly appreciated. I talked to cox' tier 2 support and they would only go as far as the cable modem. thanks in advance for any help.