Just to reiterate, wifi gets the full download speed so I don't think it's the modem. I ran a cable to the router from my pc and it got 11mbps. The same computer connected through wifi gets the full 180. Same with other pc's.
The reason I suggested connecting to the modem wasn't because I thought it was a modem issue, but a problem with the switch in the router or something with how the ethernet adapter (vs wireless adapters) were configured. It is strange that wired is slow when wireless is fast since WLAN throughput is usually routed through LAN. Disabling hardware acceleration might be worth trying even if your not using PPPoE. It's one of the few things that only effects WAN>LAN since it doesn't work with wireless clients.
Also, what is your local area connection speed? Windows Key + R > NCPA.CPL > Right click "Local Area Connection" left click "Status" > Look beside "Speed"
If it is above 100Mbps, can you give some background on the problem? Has it occurred since getting the router? Since firmware update? Installed any wired devices recently like a printer?