Hey ngnyupdownstate I want to help, so I'll share a few thoughts on this. First off, restarting phone is a good thing to do. I restart mine daily just to give the phone a fresh start. However, I don't feel like it's completely necessary to have to restart every time you go to a different part of a city for example. The other part you mentioned about going from spotty coverage is something to think about too. The phone is designed to search for networks and connect when there's coverage available. In the instance it doesn't a restart would be necessary, but this isn't uncommon.
The other pieces of the puzzle are the coverage in the area, line of site to the tower, and congestion. How we handle this is by filing service complaints for the areas where you have these issues. Our field techs will take a look at the towers and your phones connection to them to help figure out the best way to help. Just a heads up, the Moto X and Nexus 5X are Non-T-Mobile phones and this could impact you as well. I'll admit that if the same thing is happening with T-Mobile branded phones in the same area, the devices may not be the case. We do have to make sure you're aware that not all service are guaranteed to work on Non-T-Mobile phones. Non-T-Mobile phone & software disclaimer
With that being said, I want to add that your experience is very important to us and we welcome any feedback you have. If you'd still like to address this by letter, you can send it to our T-Mobile Customer Relations team on Contact Us page. Thanks for using our forum.