RX 480 8 GB crashing/perfomance issues [ Edited ]

[BTCexpert]

For the last few weeks i dont know what happened with patchnotes or drivers but my rx 480 8GB just completety struggles to play this game.

I get 100-144 fps (locked on 144fps) because i have a 144hz monitor. But the game itself isnt showing 100-144 fps. My character is walking faster then the game it stutters the whole game long and i cant even shoot.

My gpu is ovc'd to 1350 mhz and memory clock is at 2150

First i thought the ovc wasnt stable so i brought it back to default settings and the game perfomance didnt change at all.

I noticed with the MSi afterburner that my gpu keeps down clocking from 1300mhz to 700mhz and sometimes even 500mhz!

I can barely even start the game up in full screen otherwise it crashed or freezes my whole pc, and apex legends is the only game i cant play anymore!

Can someone please help me what the problem is, because i am losing my mind

EDIT: YES i reinstalled my windows & checked drivers/updated everything so there is totally nothing wrong with my PC

Specs:

ASUS z370f motherboard

i5 8600k ovc to 4.5 ghz stable

16gb ddr4 3000 mhz

256 gb SSD and 1TB HDD

AMD rx 480 8GB gaming X

[BTCexpert]

#HELP

[EA_Barry]

@BTCexpert 

It sounds like your GPU is having a cooling issue, it should not be downclocking that much.

Have you you replaced the heatsink or the thermal paste?

Did you drop the GPU possibly separating the heatsink from the processor?

[BTCexpert]

My GPU is IDLE at 55 and in game load max is 67 this card should be able to hit 90 so thats not the problem.

[EA_Barry]

@BTCexpert 

Ok, temps may not be the issue so. There is excessive downclocking for some reason.

Are your drivers up to date? Do you have a possibly misconfigured profile active via EVGA Precision or some other GPU monitoring/clocking app?

Thanks.

[BTCexpert]

I tried to look up at the AMD community page for driver issues. I saw that there was a issue with anti cheat and updating the driver would resolve it (but it didnt work for me).

Now i get a error with 30005 anti cheat, and if i start apex legends now and i get in the menu my whole screen goes black and my pc freezes (so i have to hard reset my computer).

I tried to delete the EasyAntiCheat.sys file in C:/Program files (x86)/EasyAntiCheat and restart apex legends with the repairservice but didnt work. I also did a sfc /scanow in CMD didnt work either it said the files are repaired but nothing changed. And it keeps telling me that my amdihk64.dll file is not signed so it keeps saying its an untrusted system file. So i am guessing apex is hard freezing my pc because of this file?