I KingoRooted my PL1 last year. CF AutoRoot mentioned in the first post of this thread may be a better method though:
https://xdaforums.com/showthread.php?t=2621862
Not sure if anyone is still using a S4 L720T like me but I was able to get the Oct-OS M [R3] working with full LTE, SMS and Call. At first I clean flashed Oct-OS M, then flashed GPApps, then MVNO Slayer APN. LTE would not work and the Cell Network "APN Names" was glitching in and out bad. I went back to TWRP, wiped, flashed "SprintS5_1_.zip" for APN configuration and it works flawlessly.
Message me if you want the files I have.