I was having the same problem on my 2.5 y/o cpu so i made this thread
http://www.tomshardware.com/answers/id-2948121/cpu-temps-high-applying-thermal-paste.html#17382998
I was getting same temps like you for about a month, idle temps going from 40-65C and on CPU hungry games like GTA V, DOTA 2 temps would go to 90C+ in 5min. Prime95 rockted my temp to 95C at full load in 2min
I bought thermal paste and applied it thinking it would have dried, still no change
So i applied again thinking that maybe i applied wrongly or heatsink wasnt fitting perfectly
then a guy on the thread said "have you tried cleaning your heatsink" and stupid me didnt even know that it you could clean that
So i cleaned it and now my temps are fine and back to normal for a stock cooler
In my thread i posted a video asking if it was a correct way but after some searches i found out that there is no need yo remove heatsink vents from the fan and you can just clean it without removing it
If you can get those canned air then use that to clean it however hold your fan(tip your finger on top of it) and then blow it and remove all the dust from those vents
I used natural air method that is by blowing air from my mouth and cleaned those vents with a brush(tooth brush very gently) or i have heard that there is a brush used in barbeques which is also perfect
If you have already cleaned your heatsink and the problem still exists then maybe your heatsink is loose and is not fitted properly
That's all i can help you with