FPS Dropping in Games, GPU Usage Fluctuating

EDIT: I'll put the actual solution here, it was not a driver issue that that was selected as the solution without my input... I went through all my parts working down to the bare-bones of the Motherboard and CPU (I noticed problems when multitasking in programs I.e. Chrome would dramatically cause performance hits on games that need little to run.) I presumed it was a processor problem, just to be sure (and for a little upgrade for myself) I changed both the Motherboard and the CPU which seemed to prevent all the problems occurring so there was definitely a bottleneck or failing parts somewhere. I changed to an ASUS M5A97 R2.0 and AMD FX 8320 8 Core 3.50 Ghz for those interested


A while back I did a PSU and GPU upgrade;

• 
  PSU: WinPower 500w to a Corsair CS550M (550w)
  GPU: VTX AMD Radeon HD 6670 (DDR3 2Gb) to an ASUS AMD Radeon 7850 (GDDR5 2Gb)

Before changing the graphics card I uninstalled all graphics drivers with Catalyst Control Center's built in uninstaller and then booted my PC in safe mode and ran DDU to get any remaining drivers.

(It might be worth noting on each AMD driver install it said warnings occurred; but looking at the log there were no errors.)

Once I had done a reinstall of drivers (The 13.12 AMD driver) I proceeded to download Battlefield 4, however I had large frame drops from around 90Fps to 20Fps during gameplay. I then thought it was an issue with the drivers and reinstalled the Graphics drivers with the same method as above - again I saw frame drops in BF4 and in other games too, such as TF2; so for the third time I reinstalled the drivers (Same method) however this did not improve the performance of games.

Games will run fine for the first few minutes of launching however they will start to go from 100+FPS to 20FPS randomly.

I then was discussing this on the Steam forums, using MSI Afterburner I could see that the GPU usage dropped when there was a FPS drop, here are some screenshots of Task Manager and MSI Afterburner whilst in games; (Note the drop at the end is me Alt+Tabbing to screenshot it)

Team Fortress 2: http://puu.sh/8lxD1.png
Just Cause 2: http://puu.sh/8ly9L.png
Skyrim: http://puu.sh/8lyTX.png

TF2 (With a Framerate graph): http://puu.sh/8lAbD.png

This happens when the PC is idle: http://puu.sh/8lB8O.png

Every time there is a drop in the GPU usage there was a FPS drop, sometimes the Core Clock and Memory Clock drop as well.

Continuing to discuss this on the Steam forums I tried disabling ULPS although I don't have a Crossfire setup I was told it can cause issues anyway. This didn't affect much - if anything.
I was told to try the latest drivers (14.4) this again did little so I System Restored back to the 13.12 drivers.

The CPU sort of fluctuates during gameplay, although I don't understand how task manager's graphs work.

Is there any bottlenecking going on? My system was fine before the PSU and GPU upgrade. BIOS problem, perhaps?

Specs:

• 
  Motherboard: ASRock 960GM/U3S3 (FX)
  CPU: AMD FX 4170 Quad Core 4.20 Ghz
  GPU: ASUS AMD Radeon HD 7850 2GB GDDR5
  RAM: Hyperam 8GB DDR3 1333Mhz
  HDD: (OS and Files): 1TB SEAGATE ST31000340NS
  HDD: (Games): 1TB Seagate ST1000DM003-1CH162
  Optical Drive: ATAPI iHAS122 C
  PSU: Corsair CS Series Modular CS550M 550W
  OS: Windows 7 Home Premium 64-bit SP1

3D Application Settings: http://puu.sh/8kmLU.png

This is literally my last hope of being able to fix this without having to go to a company to test my computer parts. Any help is really appreciated; I have no idea of what to do to fix this, I also wouldn't want to uninstall Windows unless it is a last resort, I have slow internet making re-downloading things an annoyance.