Contstant fps stutters and mhz drops

[Thijstp]

Hello 2 days ago I built a new PC I used the video card from my old PC in my new PC but now when I play a game I have FPS drops and I think it has to do with the MHZ of my video card all the time up and go down and also when the gpu need to do more thw mhz is dropping and how higher i cap my fps the worse it gets in a video bellow is show what i mean with mhz drops this is what it looks like in game.

 

Specs 

Ryzen 5 2600 

Asus strix rx 480 8gb 

8 gb ddr4 ballistix 2400 mhz ram

Msi b450 pro vdh max 

Coirsair Cs 750m psu 

 

I have tried

To uninstall al drivers 

Clean window install 

Took grapic card out and back in

Tryed older drivers

 

I really hop