There are various methods for doing this. I've seen various results as well. I know this might seem a little lengthy for some, but the knowledge you pick up using these other tools should prove to be helpful in the long run. These tools are powerful, and I've spent more of my time using them that flashing ROMs and other stuff since I mainly run a Cricket website.

The end result is your device having the PRL you want on it.

Required Files:

Samsung Galaxy S3 Drivers -
Support - Sprint Cell Phones SPH-L710 | Samsung Cell Phones

(Support > Manual & Downloads > Software)

DFS CDMATool (DEMO) -

CDMA Tool. DFS software. www.cdmatool.com

Required Item:
MSL - You can call Sprint or use a variety of methods to obtain it. One is in the video directly below.