I am running a Sprint L720T.
1. You want to start on the latest stock ROM. I flashed XAS-L720TVPUCOK3-20160108182710 with Odin.
2. Make sure you are fully activated on the stock ROM. Check LTE, GPS, etc are working. Make sure you do a PRL update.
3. Flash CF-Auto root with Odin, CF-Auto-Root-jflterefreshspr-jflterefreshspr-sphl720t
4. Boot into the stock recovery. Do a factory reset.
5. Flash the latest TWRP with Odin (download the tar file).
6. Boot into TWRP recovery. Install CM13 and GApps.
7. Boot CM13. Allow it to setup. Make sure you have a cell signal/service connection. You will not have data yet.
8. Reboot into TWRP recovery. Install MVNOBuzbee.zip. The script will popup a little UI where you need to pick Ting.
9. Done!. Enjoy LTE.
Note, there seems to be an issue with the camera app in CM13. The fix seems to be to "Deny" it permission to your location info. Seems ok other than that so far for my model.