I actually have a new theory. I just had a 10 bout of no service on my drive home. I had google maps active the whole 40 minute drive. The whole way down the highway, there's like a dozen visible cell sites, all right along the highway. I know I've always had good service through there and never lost it before. Now midway through the trip, as I passed within 200 ft of cell sites, my reception never went above 2 dots of LTE, strange. Then all of a sudden I started picking up different towers and reception would go up. Once I crested the top of a small mountain with a cell site located on it, i dropped to one dot, then no service. This was puzzling as I was on top of a mountain. I toggled airplane mode, still wouldn't connect and said no service. Finally, 3 miles down the road FULL reception came back of LTE and stayed that way for the remainder of the trip.
Now old blackberry devices, you were able to enter engineering mode on engineering flashes firmware. You were able to see all neighboring cells and active ones and pin point where they were on a map by coordinates. Now I don't think our engineering "field test" mode is that advanced without other software. We were able to physically choose to connect the phone to each cell site as we see fit, based upon reception and even "lock out" known weak cell sites to avoid bad connections.
Now I have a hunch that something is whacked with the current Carrier Settings and it's keeping the phone from using the closest, strongest cell sites. I bet the phone is staying connected to fast sites (hence the drastically lower reception) and is refusing to hand off properly to the next available site. Sounds like a somewhat solid theory? That could explain why the phones default to 3G or 1x. The tower the phone is trying to use is too far and it's bumping down to what it thinks is better reception but in reality, there are indeed closer towers it's refusing to see. This could explain why before when I was at work, I went into field test mode and looked for neighboring cells and the phone said "0". I must've been connected to a far tower when think there's some on the roof of the building across the street from me (county courthouse).