, i used to have this when i'm on 7300GT gDDR3. the culprit is, because i overclock way too high and leads to GPU overtemp, the catch is, even though GPU temp monitoring system (i use RivaTuner FR2.0), the GPU temp not even hit 80°C, but the card itself thinks the GPU is hot, thus downclocking the GPU to a safer clock, on this case, it'll set to 2D clock... and that is why, our 3DMark03/05/06's score... lower than stock