iPhone 6 GPS not working

Hello there,

For just about the past year (since about iOS 9 release), my phone's GPS has not been working. When I would try to use Apple Maps, it would say my car was off the road somewhere in the grass, and sometimes many roads over. It could never keep up with me while driving. This also occurred while using Google Maps, so I knew it wasn't just a problem with the Apple Maps app.

I tried to restart the phone several times, delete GPS apps and reinstall them, fully wipe the phone and start it from scratch, etc. The problem still exists. So for a while I just dealt with it. I just used my car's GPS if I needed one. Though it always bothered me that my 128GB iPhone 6's GPS was not working. However, with the release of the game "Pokemon GO" which relies on GPS, I am quite disappointed as I keep getting an error message that my GPS signal is not detected (yes, I enabled location services for the app).

Is there some app or something I can use to diagnose my GPS antennae within the phone? I have full 5-bar (dot?) signal, and my phone is in developer/debug mode, so I can also see the detailed signal strength is -81. I have AT&T as my carrier. There must be some way to determine if something in my phone is damaged. I would go to the Apple Store, but the closest one is about an hour and a half away, so I would like to avoid that if possible.