M8 Lag like hell

I have a htc one m8 lagging like hell exactly like the one in the video.
I have tried to reflash latest firmware, Hardware reset, reheat the cpu, but none worked. I tried also with another display but it is the same result.
I also noticed when i crocked the case it gets back to normal but only for few moments. Please help me and tell me what to heat/reheat/change.:confused:
Thank you all in advance.