Macbook Pro overheating issue?
So any suggestions as to why it might be happening? Is it overheating?


No, it's not overheating.  It's actually attempting to prevent an overheat condition.

Your MacBook Pro is doing two things to keep the CPU/GPU within operating temperature tolerances:


spinning up the fans, to cool the CPU
allocating CPU to lower the load demand


When you install software to override the SMC's control of the fans (cooling), you force the system to increase the CPU allocation to prevent additional load - it will become slower.

What you should do is 


clean the dust from the fans
put in new, high quality thermal paste on the CPU heat sink


There are excellent videos on how to do this procedure on YouTube