Help Please! MacBook Pro 13" - mid 2012 Running Extremely Slow No Matter What I Try

My MacBook started running extremely slow, so slow its unusable.

There is no reason that I can identify for it to start running slow, I didn't do any updates around that time, nothing but regular usage.

At that time it had 8GB of RAM and 320GB HDD (original).

The things I have tried to do to fix it are:

-backing it up, was taking too long so I cancelled it and decided to later restore using a back up from a week or two earlier.

-erased all data from HDD

-booted back up still slow

--

-reinstall OS X Mojave

-left to install over night and in the morning was still stuck at the same place I left it at

-tried a few more times even plugging in a ethernet cable

-still didn't work no matter how long I left it to download

--

-purchased extra ram so now at 16GB RAM (matching the one I had upgraded to before, Corsair 1333MHz)

-purchased an SSD ( Samsung 860 EVO Sata 6gb/s 500 GB)

-installed and tried OS X Mojave reinstall again

-didn't work

--

-tried using a usb to install high sierra

-again left for 12 hours and the download didn't budge

--

-more research led me to reinstalling the factory OS X

-used online recovery to reinstall OS X mountain lion

-left the download to run for so long I lost track of time

-finally downloaded, still really slow

--

-more research led me to taking the battery out

-no luck, still slow

--

-placed the batter back in

-next I reinstalle mountain lion

-still slow

--

-updated to Mojave (took a good 24 hours)

-still slow

I have no idea what to do next, if anyone has any ideas they would be greatly appreciated!

If I missed any info, please let me know.

[Image Edited by Host to Remove Serial Number]