Apparently there’s a known issue for Note 3 owners on AT&T whereby the GPS struggles to establish a fix or it frequently cuts out. Sometimes it drops for a short time and returns, at other times it seems to go missing for prolonged periods. This might not be confined to AT&T as there have been a few recent reports from other countries, but AT&T did acknowledge the problem and claim it was working on a fix.
- AT&T released the Android 4.4 KitKat update for the Note 3 and it seems to resolve the majority of GPS issues. You should get the update OTA (Over The Air), but you can always check in Settings > General > About device > Software update.
- You could try rooting your Note 3. Apparently the ROM in this XDA Developers thread alleviates the GPS issue.