Ibelite.com are reporting that it is indeed possible to uncap bandwidth limitations on your cable modem. Referring to other sites this was thought - and maybe still is - impossible.
Quote from Ibelite: Even though on many sites (dslreports.com,speedguide.net...) have said that this was impossible because the cap is given by the server and not found on the modem. They were proven wrong in one point - it is POSSIBLE. I for one, are an example. I have been successful - uncapping took me 20 minutes. For more info warp 2 Ibelite or Surf Board Modems for instructions.