Here is the older phone info app that allows you to turn off LTE. You will have to enable sideloading.
Details of using the app can be found here.
http://www.droid-life.com/2012/07/10/how-to-turn-off-4g-on-verizons-galaxy-s3/
Details of using the app can be found here.
http://www.droid-life.com/2012/07/10/how-to-turn-off-4g-on-verizons-galaxy-s3/