mobile

3 weeks ago I made the purchase on ebay a Sprint Galaxy S4 SHP-L720, according unlocked for any carrier, I use it in Mexico, but I have the following problems:

My galaxy s4 comes with a custom rom Wonder Negalite-Rom
the rom does not work well because the applications are automatically closed.
the version of the software is the L720VPUAMDC, and according to this version is for android 4.2.2 and I have installed 4.4.2.
I have no backup to return to a stock rom.
GPS never connected, all the time is looking for satellites
the battery is discharged quickly, I have tried others and got it.

as I can do to return to a stock rom, but since I s if the rom that I installed is the L720VPUAMDC, or upgrade to the newest.
that risk if I took the flash to L720VPUAMDC, I read that this process is phones die, and that will remove the custom recovery, and custom rom to install a stock rom.

someone who can help me with this process.

Thanks for your time !!