Question Bad Performance and Huge fps drops on a RX 580 and i3 8100

[Cardinawl]

Hi.
2 Days ago i replaced a RX 580 with my 750ti and paired with the i3 8100.
the performance has been TRASH!
pure TRASH!
i play on 768p because my monitor doesn't support higher than that( i'll buy a new one soon )
and it doesn't matter which graphic settings i set the game on,it's the same performance and same frame rate!
games i tried until now:
BF1 : 20-55 fps (with huge fps drops)
i doubled the resolution rendering to make sure there is enough load on the GPU which turns out there is absolutely no difference between ANY GRAPHIC SETTINGS I SET
R6 Siege : 70-150 (with huge fps drops)
i used the TXAA 2X anti aliasing to render the resolution on a resolution like 1080p but the result was the same as the BF1
Hunt Showdown: i shouldn't mention it because it's not released yet and it's actually on early access but the thing is i have the same shitty frame rate as when i had 750ti....and annoying fps drops of course
Csgo: 100+ thank god i don't have any problem with this one!
one other thing to be mentioned is that the CPU & GPU usages are all on 100% in all these games but the temperatures are ok (both are less than 70 the whole time)
the CPU usage was also 100% before i buy the RX 580


the most annoying thing is if i kept my gtx 750ti which was too weak for my i3 8100 , i had atleast a stable frame rate and playable performance on low quality ( since i never really cared about graphics )
PC components:
CPU: i3 8100
CPU Cooler: Cooler Master Hyper tx3 Evo
GPU: Sapphire rx 580 Pulse 8gb
RAM: 16GB G.Skill Aegis DDR4-2400
MB: MSI B360 Gaming Plus
PSU: be quiet! pure power 11 500w

 

[rgd1101]

malware scan?
check each core usage?
gpu usage at 100%? what core speed it is running?

 

[Cardinawl]

malware scan?
check each core usage?
gpu usage at 100%? what core speed it is running?

Scanned the PC once already.
all CPU Cores are on 100% (bf1 & Csgo & R6)
what i just found out is that the gpu usage in csgo is constantly changing between 0 to 80 but the cpu is always stuck up at 85%+
GPU memory clock on 2000MHz and Engine clock on 1365MHz
Here are 2 shots of bf1;

https://imgur.com/K6K25Jg

View: https://imgur.com/K6K25Jg

https://imgur.com/3za4fVg

View: https://imgur.com/3za4fVg

 

[rgd1101]

could be time to upgrade the cpu

 

[Cardinawl]

could be time to upgrade the cpu

it is not a CPU that could handle every game perfectly, i know.
most of the AAA Games are now too much for i3 8100,i know.
But still, what i saw on the Internet, every website i checked, every Frame test Video i watched in Youtube, showed that it shouldn't be this bad you know.
I don't even want to play games on ultra or even high, my Problem is the results im gettin, no matter on which Graphics i set , they are all aproximately the same. fps drops and freezes, GPU usage drops. these are things that i haven't experienced even with my 5yo 750ti
this is weird man.