Aspire 6530G graphical performance issues - cant figure this out!

Hi all,
I bought this laptop because it is able to play some games, but since a few months, it has some annoying performance issues.
In every 3D game, after a few minutes the fps rate suddenly breaks down to 4-5 fps for 20-25 seconds accompanied with an audible fan noise, then the frame rate returns back to normal. After another 2-5 minutes (depending on game), the same phenomenon happens, the frame rate breaks down for 20-25 seconds, then back to normal for a few minutes, and so on.

With the help of Ati Tray Tools, I monitored CPU and GPU activity and temperature, and it showed that every 2-5 mins, the GPU load dropped from 60-80% down to 10-30% for these few seconds. At the same time the CPU load increases (trying to pick up the slack?). The GPU temp seems to be the reason, as it steadily rises (to 65-72 degrees, depending on game), and when the frame rate breaks down it cools a few degrees and then slowly rises again.

I have had it serviced two times by Acer already, the first time they just reinstalled factory settings (great, what a help!), and the second time, they said its a faulty HDD and swapped it out. Nothing changed, though, and they havent touched the graphics card either.

I dont know what else to do, or if anyone else has had this problem, and how they explained it to Acer. The last time I attached detailed reports and game demos for them to reproduce the error, but it seems they didnt check it.

Oh, and here are some basics:
Graphics Card is Ati Radeon HD 3470 X2 Hybrid
Windows Vista Home Premium fully patched
3GB RAM, 320 GB HDD
AMD Turion X2 CPU

Here is what didnt help:
- Disabling Ati Crossfire
- Disabling all but the most elemental Windows Services
- Installing various graphics drivers (including non-certified "tweaked" drivers)
- changing in-game resolutions or graphical effects (but notably the lag effect is largest at 60-80% GPU load - when it is 100%, for example in benchmarks, the GPU fan always spins at 100% and there is not the same lag effect)
- blowing through the air vents to clean out dust

Any help, advice or thoughts are greatly appreciated!

Cheers

Yeah, thats right, power management (be it Acer ePower Management or Windows) is set to high performance.

Ok, thanks for your input all.
I ran a memtest (Gold Memory) for 5 hours today, and no errors were reported. Trying a different test (memtest86) now, but so far its clean too.

Any other suggestions what I can do?

To answer all of the questions, yes, the correct amount of RAM and VRAM is registered, and all memtests came clean. The Vista performance index reports the Graphics Card to be the slowest factor at 4.0 (which is still decent enough I think).
Oh, also, I deactivated the graphc card's hyper memory before (I forgot where it was), and it also didn't help the issue.


Sigh...

Ok, so to conclude this story, I brought it back to Acer (4th time), and after a few days they called me.
They cannot fix the issue and don't manufacture that model any more, so they offered me a newer model as replacement.
Even though the screen size is a bit smaller, its all in all a better model, and all problems are gone.

Props to Acer for the customer service!