Recently went through a period of time where my Data service didn't work when I was outside. Tried everything to no avail. It ocurred to me that my troubles began shortly after installing McAfee anti virus and VPM. I removed it from my phone and voila! Everything works just fine.
No idea why it was the source of the problem but if you have an antivirus/VPM program installed and suffer from slow connections or nonexistent connections the problem may be with that program. Simply delete it.