Scout2- I'm glad I read your post because I was just getting ready to switch to T-Mobile too. I have an S9+ and I don't want to end up with the same issue we're experiencing with Boost. I just got my phone so I'm not in any position to go out and get another one. Keep us posted on your progress w/ T-Mobile.
@scout2 It looks like Santa may have come early. I received a 770 MB update today and now I'm getting LTE around my house. I haven't been out and about to test the signal around my town but I'm hopeful.
I hope he comes to see you too! Look for reindeer tracks.