iPhone 15 Pro Max not connecting to T-Mobile 5G, defaults to Roaming LTE

I just got my iPhone 15 Pro Max today, and so far T-Mobile’s 5G simply doesn’t work on my phone. I upgraded from a 13 Pro- I had 5G coverage pretty much wherever I went where I live. Now, my iPhone defaults to “Roaming LTE”- not even T-Mobile’s network.

Under cellular settings, network selection is set to automatic, manually selecting T-Mobile doesn’t seem to do anything. I’ve tried restarting, turning airplane mode on/off, turning on/off the line, and double-checking to make sure 5G is enabled. Has anyone else encountered this issue?

Edit: I’m currently on iOS 17.0.2