Dell Latitude E6530 - Slow Performance and Freezing Windows

I have had my Latitude E6530 since Sep-2012, worked great for some time, but during the last 12 months the performance of the laptop has started to become questionable with the laptop itself becoming very hot.  Re-installed everything fresh did help for very short periods but now as of the last months or two the performance has got worse and now this week it is unbearable.  IE when trying to open tabs, load webpages they have a delay or some kind and result in freezing IE in its entirety if not crashing it completely.  Not just IE but other application as well can have a delay of some kind when trying to open or refresh pages.  Even at times the mouse will suddenly stutter across the screen, in fact as I type this the text onscreen is struggling to keep up!

At first I thought it may have been to do with the docking station not pushing through enough power, but I have noticed the fan is ramping up in speed significantly so my thoughts are now on the laptop either the CPU or even the GPU overheating.

I have spoke to DELL who are sending a replacement heatsink/fan but the performance seems permanent now, even after being cooled down overnight it can be slow from the off so I'm concerned the damage maybe more permanent and the fan may not be the full fix.

Looking for any suggestions or thoughts from the Dell community here.

Dell E6530

Intel i7

Dedicated Graphic NVidia 5200

8GB RAM

Windows 7 64bit

Cheers!