I've had the exact same problem before with my Mid-2010 MacBook Pro. I took it into the Apple support people on campus and, after running quite a few tests, they found out that the cable connecting the AirPort card to the motherboard had gone bad. It sounds like this is the same thing that you're experiencing, so your best bet is to see about getting that cable replaced.
I have a suggestion to avoid "swapping parts randomly".
Start by disconnecting all unnecessary parts from the logic board to make a "minimal machine". For example: disconnect optical drive, airport/bluetooth card, speaker (this might seem odd, but I have occasionally found faulty speakers to be the cause of issues which don't seem at all related to sound), battery, leave only one RAM chip installed.
Test the machine for a day using this minimal machine.
If you see a freeze, unfortunately the issue relates to one of the components that remain. In that situation, try to make the machine even more minimal. (The ultimate here is logic board, RAM, power input, power button and speaker... if this setup doesn't give the startup chime, one of those components is faulty... unfortunately this won't help with your intermittent freezing, but I mention it to try and illustrate the minimal machine idea a bit more.)
If you don't see a freeze, probably the issue is caused by one of the components you disconnected. Try adding one at a time, repeating the day-long test each time, to narrow down which is the cause.
An erratic airport card certainly could be the cause of intermittent freezes. Before you try the minimal machine idea (which can take some time), I think it's certainly worth testing the machine for a day with that card disconnected.
Best Answer
There was a firmware update for the MBP that addressed unexpected shutdowns...might try that and see if it solve the problem. Look here