Speed is over 20Mbps when MacBook Pro is directly wired to cable modem (however this set up is not practical for me).
This was an issue previously with Time Warner before I left Manhattan 2 yrs ago for school.
No issues using same hardware on school LAN.
No issues using same hardware with Optimum Online (Cablevision, Long Island).
Time Warner Road Runner is the only ISP that has caused this service.
Cycling modem/router relieves speed issue temporarily but it returns after a few minutes.
Everything slows, Firefox, Safari, Skype transfers, you name it.
iPhone is able to connect at higher download speed to router though is still affected.
Been searching for an answer for weeks, Time Warner customer support did not help.