OK. It worked!!! This is what I did. ( I am not responsible for sh1t if anyone does anything bad to anything, ever)
1. Boot into DL mode (power+down+home) and connect to odin, flash
metroPCS Firmware update (BL, AP and CP files AT THE SAME TIME) with auto reboot unchecked. Let it finish to "RESET"
2. Battery out. Battery back in.
3. Boot BACK into DL mode, connect to odin. Flash
TWRP recovery with auto reboot unchecked. (Not sure why it would not do it at the same time after step 1, but whatever)
4. Battery out. Battery back in.
5. Boot into TWRP recovery (power+up+home), make a backup.
6. USB connect your phone to your PC. Save the backup from the TWRP folder to somewhere on your PC. Leave the folders on the phone, just make a copy and paste somewhere for safe keeping. (you probably wont need it)
7. Replace the contents of the final folder (of the newly created TWRP backup) on your SD card with the contents of "
StockROM - G550T1 - UVU1APF1 v6.0.1 (TMO)"
For example, your backup folder will look something like this on your SD card:
SM-G550T1\Card\TWRP\BACKUPS\4200fa40da5773d1\2016-09-25--22-20-31_MMB29K.G550T1UVU1APF1/THE OLD STUFF
From your PC, you need to get rid of all that OLD STUFF on your SD and replace it with the NEW STUFF from the unzipped StockRom. So your folder on your SD card should look something like this:
SM-G550T1\Card\TWRP\BACKUPS\4200fa40da5773d1\2016-09-25--22-20-31_MMB29K.G550T1UVU1APF1/THE NEW STUFF (GET RID OF THE OLD STUFF)
7. Do a TWRP Restore (should only be one choice).
DO NOT RESTORE THE EFS FOLDER.
8. Re-boot.
That's what I did. It worked for me.