Intermittent 4G data issue
I was having these same problems on my 5 and had been speaking to AT&T regularly about it. I finally gave up talking to AT&T and decided to call apple. Mind you I have gotten a new SIM card, set up phone as new(but restored from back up) and was still having this problem. Made an appointment with the Genius Bar and decided to set up as new before I went.
This time I did not restore from a back up thinking I was going to get a replacement. Now I have 4 bars of LTE consistently(have never even seen LTE at my house before) and when phone calls come through I have 3-4 bars on 4g instead of 1-2. So far my signal has not been fluctuating like it was previously and I have yet to lose service. I also noticed that I now can use FaceTime over network and not just wifi.
I really hope this continues to work, I was getting really tired of resetting my network settings multiple times a day just to get 1-3(fluctuating constantly) bars of 4g back.