As many of you have been flashing custom ROMs; some of you have had an issue regarding broken mobile data/LTE/GPS has arisen. I too had this same issue when I was flashing ROMs and decided to post my fix. This is a guide that MAY fix your problem. NO GUARANTEES
For this to work properly you MUST be on a STOCK TW ROM. I used S3R.x's ROM but you can use whatever works for you. After you have gone back to a Stock TW ROM follow the steps outlined below:
1. Enter the Samsung service mode by typing this code into the dial pad *#197328640#
2. Then go to Mainmenu>UMTS>Common>NV REBUILD>NV REBUILD> (Important: don't exit the menu yet!)
3. Wait 30+ sec
4. Long press power button and select "Restart / Reboot"
5. Now check your GPS from any software that may use GPS like "Maps" or "GPS Status"
6. Flash your favorite ROM and go about your merry way!
Credit: S3R.x ROM Development Thread
Again this is a fix that worked for me and may not work for everyone. Also if any of this info is wrong or needs corrections, I am always open to suggestions!