Games running slower after installing new graphics card

[Metal Engie]

So some time ago I upgraded my graphics card from a GTX 970 to a RX 580, and ever since then I've struggled to hit 60 fps in games like Killing Floor 2, Doom 2016, or Overwatch. I've tried putting the old card back in, uninstalling and reinstalling various drivers, loading a backup from 2016, and none of it worked.

Some things to note:
- I am not very tech-savey (my dad's the one who got me the computer and the new card, though he only knows a little more than I do since he had someone else put it together)

- I noticed that with Doom when I set the API to vulkin the fps would go from struggling to hit 40 to way over 60, this happens on both the old and new card. Not sure how helpful this is but it seemed important to me.

And here's my specs that I mostly copy-pasted from dxdiag

Operating System: Windows 7 Professional 64-bit
Processor: AMD FX(tm)-8350 Eight-Core Processor            (8 CPUs), ~4.0GHz
Memory: 16384MB RAM
Available OS Memory: 16332MB RAM
Page File: 3220MB used, 29439MB available
DirectX Version: DirectX 11

[PyroCF]

Use display driver uninstaller (DDU) in safe mode to ensure all drivers are totally gone. Then make sure you pick up the latest AMD drivers (18.8.1 as of this psi).

The 580 should do very well in Doom km Vulkan.

[Metal Engie]

I now realize I worded the vulkan part a bit weirdly. I was trying to say that Doom runs better with vulkan than without on both the new and old card, which I thought was strange but like I said I know very little about this stuff so it could be nothing. I'll try DDU and updating drivers and edit this post with results later.

[BatHands]

It's an upgrade depending on what you're playing. If you get the RX 580 with 8GBs you'll see performance boost.

It's better here

https://img.purch.com/r/711x457/aHR0cDovL21lZGlhLmJlc3RvZm1pY3JvLmNvbS9ML1MvNjY5NTIwL29yaWdpbmFsL2Zwcy5wbmc=

and worse here

https://img.purch.com/r/711x457/aHR0cDovL21lZGlhLmJlc3RvZm1pY3JvLmNvbS9ML0YvNjY5NTA3L29yaWdpbmFsL2Zwcy5wbmc=

[Metal Engie]

Yeah some googling I did said the same thing about being more intensive, so I guess the 580 is a no go. I suppose my goal now is to get the 970 to work like it used to, though I'm not really sure where to start on that.

[Curls]

If for whatever reason you can't refund it you could always have both GPU's in the same computer and just run the game off the one that runs the best

ridiculous as hell but you already got it. Probably better just selling it