Airport losing connection consistently

I have a 2006 macbook CoreDuo. I ran into a diminishing airport reception problem like many I've read about on the web. I changed the airport card a few months ago and the problem persists, with a little change to it. Instead of steadily losing bars of reception, now it works fine until it drops the connection, when I try to reconnect to the basestation it asks me for the password again, even though it''s saved and can , access it at other times. Then it times out trying to connect to the basestation. It cannot connect to the basestation again, unless I put it to sleep, or restart it. Restarting it results in a longer time that I can stay connected before it drops again, but putting it to sleep even for seconds will allow it to reconnect again, with me doing nothing at all.

The thing I think is causing this that I can tell is the temperature. It happens predictably when I am streaming video, as this gets my machine hot and the fan working at maximum.

I've also started to have Random Shutdowns as I've read about that were happening in earlier model Macbooks than mine, that were being caused by heatsink problems and were corrected in a firmware update.

All of this leads me to believe I have a problem with my heatsink or airport card wires running over a heatsink, something like that. Does anyone have an opinion on this.

I know it's a little convoluted but I've been living with this airport problems for about a year now, since before i installed the new card 6 mos. ago.

Thanks for your help