New computer decreases games performance after a few days

PC Specs:
i3 6100 3.7Ghz with the stock cooler
PowerColor RX460 4GB VRAM
2x8gb Kingston DDR4 2133mhz
MoBo Asus H110M-C
PSU Corsair CX600
HDD Seagate 3,5 1TB
W10 Home SL

Howdy guys,

I've been experiencing some issues when playing Battlefield 1. I do know the i3 is below the minimum reqs. but it performs well and I'd say it is doable.
The issue is, the first time I set up everything with W10 I was getting a normal CPU usage and GPU usage when playing (around 80-85% CPU and 90-99% GPU).

All of a sudden, with no apps installed and no settings changed, my GPU started to drop its usage to 70-75% during heavy fights. My frames would fluctuate from 70-80 to 55 for a second or two and still I don't know why it didn't happen when I first installed the OS.

Not to mention that if I change my resolution to let's say 1600x900 or even 1366x768 the usage keeps under 80% and sometimes less than 70% and the drops to the 50's still happens, as if I had a bottleneck going on. My temps are somewhat okay I think, the i3 never got above 60ºC and the GPU is around 68-75ºC.

Right now I am having drops to the 40's when playing a certain map, which is not the most demanding one (St. Quentin's Scar is the map, before these mentioned problems I had frames ranging from 65 to 110). Some desert maps, which are the least demanding ones, are dropping my gpu usage to 60% (around 55-60FPS) during heavy fights but when I look to the sky or mountains it gets the usage back to 95% and frames around 90-110.

Just to remember that when I am checking my temps. with Afterburner I have this 'unified something option' enabled.

So far I've tried different things:

- Set the game to DX12 and found out that the GPU usage stabilizes even when playing on lower resolutions like 1280x720 but it stutters a lot because of the CPU usage always around 95-100% (capping the frames doesn't help at all);
- Disabled the Virtual Memory (enabled it again);
- Disabled the HT (enabled it again as well);
- Uninstalled all built-in apps, disabled Windows Defender, Windows Update, XBOX DVR, Cortana;
- Disabled the Origin in-game overlay;
- Unparked my cores (no performance increase or decrease, parked them back);
- Set the Power settings to 'High Performance';
- Updated my BIOS;
- Tried both W10 and W7, the issue persists on both;
- Disabled Speedstep (no changes at all);
- Changed the RX fan speed from Auto to 90% just to be sure, still dropping to 70% gpu usage;
- Disabled the driver update system W10 has;
- Set the Wattman power limit to 50+ (is that right?);
- Set the BIOS to Default as well as Crimson's settings.

The programs I have are:

- Steam);
- Origin;
- Battlefield 1;
- Teamspeak;
- Realtek Audio Driver (I am pointing this because some people years ago had problems with Realtek iirc, and they still have in games like World of Warcraft);

Crimsons I already installed and uninstalled:

WHQL 16.11.4 - Gave me the most durable performance, lasted two days before things started happening again;
WHQL 16.12.1 - GPU usage keeps dropping when joining matches and when deploying, leading to a lot of stuttering;
NON-WHQL 17.1.1 - No performance increase at all.

I have uninstalled all of them with both DDU and AMD Cleanup Utility.

I have no idea what is going on with this pc.

Any ideas?

Thanks in advance.