FSX Major Lag Spikes - CPU?

Hi there, sorry to bother everyone but this is really bugging me now!

 

I've been having this issue with FSX where my frames are running fine and then suddenly drops down to 2/3FPS for about 30 seconds. Which, clearly isn't right. 

 

It all happened after I installed Aerosoft's Airbus X Extended, it happened to me before but I was never able to fix it, and then I put my system back to Windows 7 and now I'm back on Windows 8. FSX had been running perfectly until I installed that aircraft, then, it started to grab all of FSX and drop everything down.

 

Here's a video: 

 

After investiagting for a little while, we found out that my CPU clocking had been dropping from 4.36GHz to 1.36GHz for those 30 seconds of frame loss.

 

Someone mentioned that my CPU was over heating, but my CPU has been running between 40% and 60% which is usually for my PC to run at during the time FSX is on.

 

Here is my system:

AMD Radeon 6670

16GB RAM

AMD Bulldozer CPU

AMD FX™-4170 Quad-Core Processor at 4.4GHz

Windows 8 x64

 

Anybody able to help? If you need more questions I'm willing to answer them!