Is anyone else having buffering issues?

Have you measured your download speed at the back of the TV and also near your gateway?  Perhaps the TV is too far away and perhaps you could find a better spot for the gateway.  (Use the Speedtest by Ookla app on your phone, connected to your Wi-Fi.)

If you home is larger, you might want to try adding a mesh network.  You can do this on your own, or I think T-Mobile is now offering that as an upgrade to TMHI service.