VCore lowering drastically (momentarily) on high CPU load

[Zipppy]

I've been having an issue ever since I got my new PSU, the new EnerMax one I've been talking about a bit, and it's that the VCore drops approximately 0.10V on high load (happens on graphically intensive games especially). It holds the voltages for everything else much better than my previous PSU, some cheap generic one I had to work with, until I had enough money to buy a proper one.

While this drop happens, my CPU underclocks to 800 MHz from the normal 3100 MHz for a couple seconds then goes back up to regular speed (read by CPU-Z), I've also tried forcing the voltage to 1.30 through the BIOS, no difference, it still does the dropping and it underclocks the same amount. The temperatures of when it's on load is about 50 degrees Celsius, on idle, it's around 40, maybe even less if it underclocked on idle.

My specs are below

ASUS M2N68-AM Plus MicroATX motherboard
ASUS EN GTX560 graphics card
EnerMax EMG700AWT PSU
AMD Athlon II X3 445 Rana (running stock at 3100 MHz, with 15.5 Multiplier forced via bios, seems to drop the multiplier on load)
Windows 7 64-Bit

I would like some insight on this issue, since every other power output doesn't drop when this occurs.

[[TC] Stephen]

Try putting the power profile on 'high performance' when you run demanding tasks. Windows is probably seeing that the CPU isn't doing much and underclocking/undervolting it to save power, but from what you're saying it seems to be quick to judge the CPU usage.

My CPU does the same thing if I leave the power plan on balanced or power saver, underclocks to 1.6ghz from 3.4.

[Zipppy]

I have it on Performance mode, Cool n' Quiet is disabled too, I'm thinking it may either be the power supply, or the Bus speed lowering itself randomly somehow.

Scratch that, I just saw the multiplier lower on a lag spike, ugh.

[Zipppy]

So setting the power plan to "Balanced" improved the matter... why does this happen? Another example, is using "power saver" on my netbook, and it gets better performance than "High Performance", and everything works better, yet the battery lasts longer...

[Zipppy]

alright, further bump here, I'm starting to think it's hardware related, I ran a CPU stress test program, and it got the same issue after about 5 minutes. I had plans on replacing my motherboard for a while now, and almost have enough to buy a very good one, and I wonder if it improves anything.

[[TC]»Elmo«]

Sounds like the CPU thinks its getting too hot and is throttling back to prevent damage.

Quick search found me this: "Maximum operating temperature 55°C"

I'd take a look at the state of the cooling - make sure there's no dust, check there's good airflow in the case etc. If it's still a problem, try getting some thermal paste (Arctic Silver 5 is good), and re-seat the cooler.
If that doesn't help much, I'd consider getting a better cooler (assuming you're still using the stock AMD one)

[Zipppy]

I'm thinking it could be the thermal paste, as I blasted out every spec of dust I could see with an air compressor. The temperature barely reaches 50C on load though, and I'm using an aftermarket cooler (Antec Kuhler 620 with the provided fan) that should lower the temperature a bit further than stock in theory. Possibly a core reaches the said temperature, and with stock cooling, the CPU shot up to 60C, and it never did this lag.