If you have a Lumia 1520 (RM-937) you should flash the 059V4M0 rom.
It's already 8.1 and net nonitor works even with the newest Dev Preview build.
Inside this rom you have the ability to even choose some or your needed radio bands.
For example you can build a "use only WCDMA and LTE" Radio band selection. It automatically switches between WCDMA and LTE. How cool ist that?
Start with dial code ##3282#.