Here is the link to the working release: http://forum.xda-developers.com/showpost.php?p=59744479&postcount=1
I had been having the most difficult time upgrading to the official Cyanogenmod 12 and having it work with LTE service. APN's were set up correctly but no LTE service just 3G.
I had been using the methods I traditionally had done by going back to the original Sprint Samsung Touchwiz build (used a default recovery build) and making sure that LTE worked as well as updating the PRL and Network Profile. I also made sure the GPS was working.
Then I would use ClockworkMod (CMW) to install the Cyanogenmod 12 nightly zip for the Sprint Samsung S4 (SPH L720). Unfortunately every time I did the install LTE would not work. I played around with the APN settings but no luck.
I finally decided to do a clean wipe and install TWRP recovery and install the AntaresOne Cyanogenmod 12.1 optimized ROM. It worked perfectly with the install. I don't know why the official nightly Cyanogenmod12 didn't work with LTE, I'm assuming it may be because I dirty flashed over the original Touchwiz build, or that the recent Cyanogenmod 12 nightly builds have a bug.
In this build there is no APN settings in the network settings so you have to use Gesture search app or maybe the APN App to manually change the APN for Ting to add "default," under APN Type next to MMS then check the box for TIng to select that APN. The initial install automatically says LTE, but don't believe it as when I tested the speed it was only 3G speeds and was probably on Sprint's 3G network and not LTE as it says in status bar.
Hope this helps.