Chosen Solution

GPS and 2.4G band functions share the same antenna: the top bezel itself. I would suspect the double L shaped antenna cables visible on the very top. Or the contact clip connect the logic board to the top bezel beneath the standalone 5GHz antenna.

I had similar problems.

  1. My bluetooth signal was weak, but not as weak as yours. For example, my bluetooth headset kept cutting out and my phone needed to be very close to the bluetooth device (headphones, car, speakers).
  2. My wfi was weak. I was always able to connect and home and at work, but the wifi is weaker than other iphones. My phone doesn’t find as many wifi hotspots and the signal cuts out more often. You note that your wifi was pretty good at home, but you should compare with other phones (preferably the same iphone model) to see if your phone isn’t recognizing as many hotspots.
  3. My GPS problems are identical to yours. I replaced the antenna from a part on eBay. It didn’t do anything. I next purchased the double-L antenna flex cable, also from eBay. It worked for a week (found more wifi hotspots, GPS worked, and bluetooth was improved), but it stopped working again. In summary, I think my problem was the antenna flex cable, but I’m not sure. It’s possible that a higher quality flex cable could be the solution. Good luck.