Windows 7: Just installed new mini card on laptop....

I have just installed a new mini card on my laptop to increase it's download capacity.

The problem I seem to be having is that my link speed seems to be intermitently jumping from my new speed to my old speed, and it also seems to be very unstable.

Is there anyway I can stop it from going back to my old link speed and stay on the new link speed?

Not sure if it is relavent but when I am not using the web it seems to be stuck on 72mbps, but when I use the internet it seemt to increase to over 100mbps.

Is this the way mini wifi cards work on laptops, are they normaly working at 72mbps and somehow when you need bandwidth they use more than one channel to get more bandwidth.