Install Drivers for Samsung Galaxy S3
Ensure previously activated (used) Verizon 4G LTE SIM is inserted into device during flash. Phone may be flashed without a SIM card, although data will work, data signal may not be seen and phone will show a notification that a SIM should be inserted.
Android 4.1.2 Open Dial Pad
At Hidden Menu Screen Select Hidden Menu
Select Enabled and Press OK
Next, press back to bring up the dial pad.
Select Qualcomm USB Settings
Select DM + MODEM + ADB or RNDIS + DM + MODEM
Press Back Till Phone Is At Home Screen
Phone Is Ready To Be Provisioned
(Remember after flashing to return and put phone back to MTP+ADB)
Open the dial pad
Enable DM Mode