I have tmobile when inserted the simcard in my z2 I've noticed that I'm not getting any internet connection so i went to Setting/wireless and networks/internet setting and downloaded all the files then I went to mobile netword and changed it to 4G Tmobile, starting that day I keep losing connection every time I have to go to mobile network and change it manually although it's set on automatic, most of teh times 4g doesn't work and I have to set it to 3g... it's really annoying
One thing I would do, is to call T-Mobile and register the IMEI so they can provision the unit. The settings on their end may have something which is preventing it to connect to it based on a previous phone's capabilities.
I had something similar similar but it was with AT&T. In my case, it would not connect to LTE at all as it would stick on HPSA. This was because I had a S3 (UK version), which was only capable of HSPA+, and I had registered the IMEI with them prior.