The speed you claim you're getting sounds suspiciously like you're measuring the speed based on a Wireless G connection. 54Mbps would be a rather strange speed to set a Cable modem to. That would require DOCSIS 3.0 to achieve anyways. Click on the two links below, running each test one after another and posting up the results from both. Since you're using a Cable connection, you cannot trust any speed test due to how Cable companies use PowerBoost. This will inflate the results. What we're looking for is the speed for a long term download, not an initial boost. The download test will download a 100MB file. Should be large enough to kill off PowerBoost and allow the test's speed measurement to level off at your true connection speed.
If all is set up correctly on your PC, you should be able to max your connection out. Their server is in Dallas, TX. At the end of test, you will be sent to a page that shows your speed. Send us the links to the images provided. ***I STRONGLY SUGGEST PLUGGING YOUR PC INTO YOUR ROUTER VIA ETHERNET FOR RELIABLE RESULTS***