2011 27" iMac wireless stuck at 54Mbs (G Speeds on N network)

Recently bought a 27" iMac and no matter what I do, the wireless won't connect on anything but 54Mbs speeds either on G or N networks, but my 2010 13" MBP connects to my N network at 300Mbs no problem, same with a friends 2010 15" MBP that I asked him to bring over for a test (connected at 300mbs on N no problem)...

Netgear WNDR3700 DualBand Router

Router has an Atheros chipset

Wireless G - set at 54Mbs, WPA2-AES security, Channel 11

Wireless N - set at 300Mbs, WPA2-AES security, Channel 161

DNS: 8.8.8.8

IPv6 is Off

2011 27" iMac

Atheros wireless chipset

Currently connecting to the router over G network because if I connect over my N network, it'll connect to the router, but have no network activity. Everything times out or doesn't load at all.

3.7MB/s peak transfer speeds

DNS: 8.8.8.8

IPv6 is Off

2010 13" MBP

Broadcom wireless chipset

Currently connecting to the router over N network

20.1 MB/s peak transfer speeds

DNS: 8.8.8.8

IPv6 is Off

Things of note:

• G network @ 54Mbs = all computers connect and have full network activity

• N network @ 300Mbs = all computers connect, only MBP's (both 13" and 15") would have actual network activity, iMac everything times out

• N network slowed to 54Mbs = all computers connect and have full network activity

• Distance to router not an issue, it's one room away

• Both computers are running Lion, but had same results under Snow Leopard

• Need 300mbs (N network) because of a network share drive. G speeds take way too long to transfer files

• I've tried every channel available, same results.

• It's not a setup issue since 2 MBP's connect at 300mbs no problem, only computer with issue is the iMac

• Trashed preferences, reset keychain, Clean install not an option. It's behaved like this straight out of the box

ideas?