Not necessarily, the NB has to work along with the gpu. I'm not as experienced as these guys around here, so it's hard for me to explain (I forgot how

), but what you are describing use to happen to me all the time, until I bought a NB cooler with a fan.
Oh yeah, I just refreshed my memory with google! The NB handles the data transfer from the ram, cpu, and gpu. The more powerful cpu and gpu you have, along with the more ram you have, the NB has to run harder. 8gb ram, an E4500, and a 3870X2............ the NB could very well be overheating. What motherboard does that have? What's the NB chipset?
http://images.tigerdirect.com/skuima...9102-main2.jpg
Is your board like that? Are those chipset coolers still functioning?