[T-Mobile Samsung Galaxy S 5] Iota1942:
Hello all, forgive me if this has already been posted somewhere but i cannot find the answers, I am desperately trying to downgrade Marshmallow to Lollipop so I can install CM 12. This phone i had purchased from Amazon so it already had 6.0.1 installed and seems to have already had the bootloader unlocked so I rooted straight out the box without a problem, though I later realized that CM 12 was not compatible with 6.0.1, so then I had "unrooted" (I simply used SuperSU Full Unroot Method) and appears to have been unrooted, I had shifted between using Odin 3.09 and 3.11.1, I dont know if that makes a difference, I had already downloaded what I believe are the STOCK firmwares for 5.1.1, but Odin cannot seem to flash them onto the device.

Here are the device details:

Model Number: SM-G900T

Android Version: 6.0.1

Android Security patch level: May 1, 2016

Baseband version: G900T3UVS3GPK3

Kernal Version: 3.4.0-7500527, dpi@SWHD7416 #1, Thu May 5 16:18:20 KST 2016

Build #: MMB29M.G900TUVU1GPE1

SE for Android status: Enforcing, SEPF_SECMOBILE_6.0.1_008, Thu May 05 16:23:03 2016

Security software version: MDF v1.1 Release 6, VPN v1.2 Release 6.1

KNOX Version: KNOX 2.6, Standard SDK 5.6.0, Premium SDK 2.6.0, Customization SDK 2.6.0, Container 2.6.0, CEP 2.0.1, Enterprise Billing 1.2.0, OTP2.6.0, SE For Android 2.4.0, SSO 2.5.0, Shared Devices 2.6.0, TIMA 3.2.002, VPN 2.2.4

First I rooted using this guide:

https://xdaforums.com/tmobile-galaxy-s5/general/root-how-to-root-sm-g900t-firmware-t3358190

Then I simply "Unrooted" using SuperSU.

I had tried using files from here:

https://xdaforums.com/tmobile-galaxy-s5/general/compilation-s5-g900t-stock-firmware-t3042400

And later Flashed the ROM in this guide using TWRP:

https://xdaforums.com/tmobile-galaxy-s5/development/how-to-update-to-g900tof6-5-1-1-pc-t3141404

And ones I have found on sammobile.com

After that I've simply been trying to wipe/reset, and use Odin to downgrade, but it fails everytime, and at one point I used the "recovery" feature when you first initialize the phone as if for the first time and it download all of my apps from my old phone, and somehow it was rooted again(?) Here is a description of what it says in Download Mode:

ODIN MODE

PRODUCT NAME: SW-G900T3

CURRENT BINARY: Custom

SYSTEM STATUS: Custom

FRP LOCK: OFF

KNOX WARRANTY VOID: 0x1 (2)

QUALCOMM SECUREBOOT: ENABLE (CSB)

RP SWREV: S1, T1, R1, A3, P1

SECURE DOWNLOAD: ENABLE

UDC START

SW REV CHECK FAIL : [aboot] Fused 3 > Binary 1

After this I simply reboot the system using the same method to initiate download mode. The boot sequence always hasSecurity Bit: Kernal up at the top when ever I reboot the system.

These are the files I have tried using in Odin 3.09 so far:

G900T3UVU1FOG6_G900T3TMB1FOG6_TMB

> G900T3UVU1FOG6_G900T3TMB1FOG6_G900T3UVU1FOG6_HOME.tar.md5

G900TUVS1FOL1_G900TTMB1FOL1_TMB

> G900TUVS1FOL1_G900TTMB1FOL1_G900TUVS1FOL1_HOME.tar.md5

G900TUVU1DOB1_G900TTMB1DOB1_TMB

> G900TUVU1DOB1_G900TTMB1DOB1_G900TUVU1DOB1_HOME.tar.md5

I have made sure they were complete downloads and have been using these files AS IS, I don't know whether or not I am supposed to rename them or anything.

Up at this point I no longer know what I am doing or what I had even flashed, I really don't know what I did wrong at this point. The biggest reason why I want to downgrade to 5.1.1 and install CM12 is because I have read that it is one the most stable custom ROMS available, hence the dire need to downgrade and REALLY want a good custom rom instead of STOCK android firmware.

If anyone would be kind enough to spend a little bit of your time to point me in the right direction I would greatly appreciate it,

OR if anyone can definitely recommend a VERY STABLE customizable ROM that would also be appreciated, as that would toss out the need to downgrade. Again, forgive me for such a long post, Thank you for your time.