I own a 5970 black edition, the core clock remains at 400mhz even under heavy load. My cpu's voltage and core speed seem a little lower than it probably should be during gameplay. Since both of these items seem to have the same problem I have begun to assume the problem must come from the motherboard but I have no idea what EXACTLY could be causing this problem.
P.S. I have also replaced the GPU and still received the same results.