MBP 1.1 bandwidth problem

Hi,

I have a MBP 1.1 with OSX 10.6.8 and when connected to my 802.11g network my bandwidth seems to be capped at 10mbps , we have 40mbps internet from brighthouse and other computers on the network get the full 38-39mpbs on the same wireless channel. When i switch to the 802.11a 5ghz network from the same router i can get around 17-20mbps while sitting 10 feet from the router. When i plug the computer into the router i get the full 38-39mbps. This is starting to blow my mind, it seems the airport extreme card is limiting the connection. any input would be greatly appreciated, google hasnt gotten me anywhere so far.....

 

-on 802.11g , channel 11 the nearest neighbors router is on channel 9, transmit rate 54 and rssi -50, 18.09mbps down / 3.01 mbps up

-on 802.11a channel 44, rssi -67, transfer rate 48, 20.3mbps down / 3.66mbps up

I have used cocktail to lock the duplex to full which i have heard is a problem, on osx 10.2 but not 10.6.8m. Cocktail boosted me from a straight 10mbps no matter what connection to the current problem.

I just tried disabling the 5ghz on the router to see if that was the causing the bandwidth to be what i think is exactly half of our full speed. No change . blahh again we have 40/5 internet and hardwired 39.55 / 4.56

 

any suggestions would be fantastic