Solved and working, guide to help others
Originally Posted by ecs87
For the millionth time...use Odin! I've posted a link to it in my Dropbox account in a few precious threads or you can get it from Sammobile. I dunno why so many people are fudging around with custom recoveries and different rom files when all you need is the MK4 firmware and odin... wipe data and cache after odining and I guarantee you you'll be fine.
Sent from my SPH-L900 using xda app-developers app
Okay, this worked for me.
Just a helpful guide for people also stuck in my boat:
Sammobile does not currently have the firmware for SPH-L900 as hotfile is offline or whatever. So I finally found the file ecs87 mentioned in his dropbox, located in this thread here:
Next I downloaded odin, choosing the "ODIN v3.09, v3.07, v3.06, v3.04, v1.85, v1.83" option, from this thread:
*EDIT* Also, you need to install your phone drivers. I had them installed already so I skipped that part. I believe you can get them from installing Kies, but not 100% sure. The guide linked in step 6a has a link to drivers, but not 100% sure if those are up to date, or working, although I'm fairly sure those are what I used a year ago if I'm not mistaken!
Steps I took as follows:
Step 0: Unplug your phone from your computer, get into download mode. (Power off, hold volume down + home button, then power button, and keep holding until a screen pops up saying caution blah blah blah, next hit the volume up key to put your phone into download mode)
Step 1: Unzip the L900VPUBMK4_L900SPTBMK4 file you downloaded from ecs87's dropbox account.
Step 2: Unzip the Odin download and choose version 3.07 (not sure if others work, but that one worked for me!)
Step 3: In Odin, click on PDA, and browse to the L900VPUBMK4_L900SPTBMK4_HOME.tar.md5 you unzipped in step 1
Step 4: Plug your phone into the computer via USB, making sure you are in download mode!
Step 5: Click the check box next to PDA if it isn't already checked.
Step 6: Make sure on Odin it says something like 0:[COM3] (Com3 was for me, you might be different), and make sure the color is blue
Step 6a: Follow these instructions for pictures if you would like as well! http://tinyurl.com/odinguide
Step 7: If the box is blue, and you've followed this guide correctly, click on start, and it should go though all the steps and you'll have 4.3 installed!
Hopefully this helps anyone who was stuck like me!
Also, thanks again to ecs87