It was rebooting on the original power supply as well, but it was only 350w. That's what I thought was causing the reboot since the graphic card requires a higher wattage power supply. WIth the old PS in, the game would reboot after about 5 minutes of play. With the new PS, it only reboots during times of "high demand".
When you say run a benchmark, do you mean something like 3d benchmark?
Thanks for your help!