I thought just I had a busted one. So i tried another one, same thing.
I asked some people who would know, and eventually got a long story filled with fussing and feuding, that ended up being T-Mobile not correctly identifying the network to the phone correctly in the areas they switched 2G into LTE yet. That will happen eventually, they just haven't got to it.
This is also why T-Mobile quietly stopped selling the HTC 10. A fully branded, filled with bloatware HTC phone will have the APN data needed to switch correctly. An unlocked model will use generic apn settings
Did some very minor googling and found this page:
https://support.t-mobile.com/docs/DOC-25898
While my unlocked phone is on "fast.t-mobile.com" automatically, not all the setting in that automatic selection match up to the manual settings described on that page. Would manually creating the access point with those settings help in any way?