ATI`s do have heat issues, If possible leave 1 or 2 slots open below the card and leave out the PCI covers to allow air to pass out the rear.Ive even went as far as mounting a fan that will push air across the card and out the open slots.I have a AIW 9700 Pro card that i actually replaced the fan on i used 1 of the fans from a Hard Drive Cooler .It didnt bolt into the heatsink cavity but i found the proper lenght of screws and mounted it to the heatsink centered above the fan cavity.
I would run memtest overnight to rule out any memory issues.
Prime 95 is another tool to use for testing hardware overnight .
I run my ATI card on 1.5 volt setting in bios. Check and see if disableing FastWrites in the ATI CP helps .
