IMac Intel 24" - Airport Wireless Rate

Question

Here is my setup:
1 - 24" Intel iMac 2.33 / 2 GB (Located 10 feet across from AP against a wall, in a large apt complex) Avg rate 13mb. I typically sit in front of the computer in between the AP and the iMac, though I see this low transfer rate without me in front of it and if I pull it out from the wall.
1 - Airport Extreme N Mounted 6 feet off the floor on opposite wall)
I have WPA2 Personal setup and WDS as Main, it is running firmware 7.3.2. There are 8 wireless clients connected (2 Macbooks, 1 Tivo, 2 iphone 3G, 2 AppleTV, 1 Wifi Cam)
1 - Airport Express N Located 5 feet to the left of the iMac on the same wall, connected to network via WDS, used as wireless bridge for HP Laserjet Printer (Average Rate 54mb)
Using iStumbler I have identified on average 8-14 other wireless networks in my area. I have adjusted my AP channel, moving it from crowded channels such as 6 or 11 to 3, 4, 10, 8 and 9... trying to keep at least 2 to 3 channels between my channel and the others I see.
Channels 1,2,3,4,5 and 10 don't work to well.. sometimes the iMac can never reconnect to the AP if these channels are selected. I have to use my MacBook to adjust the channel back a different channel... its pretty hit and miss... sometimes it works... some times it doesn't. The transfer rate will start out high... 120 and than drop settling on 13 no matter what channel with or without IR turned on. I avoid IR as it can drag down performance on its own and with 8 wireless clients already pulling on resources... I just avoid it.. doesn't seem to solve this issue.
Also, my Macbook Pro and MacBook can be positioned in the same location as my iMac and still maintain transfer rates of 120-130 on average.
I do not have a wireless phone in the house and the microwave is located on the other end of the apartment. the only thing near the AP is a LCD tv 3 feet below it. I have an external MyBook Drive sitting next to my iMac along with a HP Laserjet printer and ScanSnap Scanner... these devices are sitting level or below the imac... there are no shelves located in close proximity to the top of the iMac.
One other thing I am noticing... Airport Utility on my iMac has difficulty locating my base station at times even with full strength indicated in the menu bar.
All other devices connected to the AP average 54 -130 mb/s - This includes my AppleTV that is in a different room and has to transmit through a hollow wall. As well as my Tivo and Wifi cam.
The AP is set for 802.11n g/b compatible... though I have tried playing with this setting as well... not all of my network up to the N standard.. Tivo for example does not have a 802.11n adapter yet.
I have read through several support postings on various Mac Support Sites as well as this one... I have reset the SMU, deleted related Pref files and recently I did a Archive and Install of the system. At one point I did roll back the firmware on the AP based off feedback others had posted... no luck.
I have a feeling this is a hardware issue, either the Card in the iMac is bad or the Antenna is damaged or faulty.
I am looking for other suggestions... I want to avoid taking my computer in for repair as often it they come back in worse shape than when they went in...
Signal Stats
Strength/Nose
iMac -43 / -95 13mb/s
Airport Express N Printer WDS Printer Bridge -36/ -92 54 mb/s
MacBook -27 / -96 130 mb/s

Answer 1

it's actually working now, don't know how but it is.
still though, airport iMac shows 40 as peak connection in AirTrafficControl and right beside it the Macbook shows a peak of 55-56
wow.