Check the power wire from the ign. switch and see if it has a bad connection. Almost sound like your ign is losing power. Also check the ground as well.
What he said. Just up and dying (without losing power first or stumbling) is going to be electrical in nature. Just need to snoop and find out why. Do your headlights also blink off wehen this happens? Gages/radio die also? Or is it just engine?