Windows 7 - BSOD 124 only during gaming, not during stress test

A while ago my computer started freezing when I was playing games. What happens is that my monitor loses video feed and turns black, the sound starts stuttering, and I have to restart. This happens with games like Bad Company 2 and the Crysis 2 demo. With Crysis 2, it freezes within 10 mins of gameplay every time. Memory dump indicates a 124 error, which is traditionally a hardware problem.

I've run a variety of stress tests on cpu, gpu, and memory and there are never freezes or errors. Nothing is overclocked. If it is indeed a hardware problem then I don't understand why it doesn't show up during stress tests. Could it be some kind of driver issue or something to do with memory that only happens when gaming?

Other things I've tried:

Opened case for airflow
Fresh windows install
Increasing voltage to cpu or memory
Removed sound card and used onboard sound
Uninstalled antivirus program
Flashed motherboard bios
Installed earlier video drivers

My specs:
Windows 7 Ultimate edition 64-bit
Core 2 Duo E8400
Asus P5Q Pro
Radeon 4870
Asus Xonar Dx

Anyone have any suggestions short of switching out parts? Thanks.

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