Low-power 3D clocks and driver recovery issue - GTX260

So I've been running my EVGA GTX260-216 for quite a while now (over a year, maybe closer to two years). It gets used for folding primarily, and also for games in as a secondary gaming rig for the occasional lan party and such.

It started giving me fits when I changed it from one older PC to a newer one. It is currently in a Biostar A770E motherboard with an Athlon II X4 640 CPU, 4GB DDR2, Antec Earthwatts 500W, Windows Vista Ultimate 64 bit, 260.99 drivers.

It'll run at full 3D clocks anywhere between 8 and 24 hours, then the display driver will hang and recover, at which point it is locked at low power 3D clocks until reboot. If I try to use rivatuner to force full 3D clocks, it'll just BSOD the PC.

Previously I was running XP Pro 32 bit and had the same issue.

I've tried lowering the clocks, that didn't help. Thought it was getting too hot, but it gets maybe 65C, and keeping it cooler didn't help. Tried swapping the power supply, nothing. I changed drivers, nothing. Even changed the OS, didn't fix it. Tested the RAM, changed it around, nothing.

I'm thinking the card is dying on me, except it seems a little odd that it would start this at the same time I moved it from one PC to another. It had been quite happy in the previous box. The only differences I can see is it was on an x8 slot instead of x16, and it is on an AMD chipset now instead of an intel. But the chipset shouldn't matter, and I would think a full x16 slot would be better than the x8, so.... :shrug:

The card was a gift, so I have no idea if there is any warranty or not.