I would look into power. grounding and PSU. I don't know of rocketfish - but are they reliable? if your psu is not putting out stable energy, it doesn't matter the wattage. your video card seems fine by objective standards, so it makes me think something else is changing when the gpu posts, and that could be power fluctuations. you don't have one to test with do you?
edit:rocketfish is a best buy brand. even if it's not the cause, I would ditch it. your hardware is too important to let a best buy/dynex bastard child destroy it.