As much as it sucks, that sounds like the GPU for sure
. If the problem persisted across an entire build, and the BSOD mentioned a video error, it sounds like that for sure.
Are temperatures getting too high on the card, possibly? You might want to download GPU-Z and enable the logging feature, and when the PC goes down again, boot back up and check the log.
If heat's not the issue, then it's worth digging deeper. Happen to have a friend that has a spare GPU kicking around to test? Does the crash seem to happen at a specific spot?
Issues like these are painful.