Capped speeds w/ new wifi card???

I recently replaced my Intel 3945 w/ a Gigabyte GN-W101GT (Atheros AR5005GS) wifi card. Before I did the switch, my Intel would get speeds around 17Mbps and hold steady (although if you took it 10 feet away from the router, it would decrease dramatically). After I switched the cards, my Gigabyte gets MUCH better range but gets 10Mbps and never any higher. When I test the connection speeds, I get to 10Mbps very quickly, then all of a sudden it will just hold there (as if it could reach higher speeds, but it's capped somehow). Tested a wired connection from the router to the laptop and will hit 17Mbps no problem. Any reason why all of a sudden I have a speed cap on my wifi card?