Question about Tmobile LTE for 5.1.1PR

Hello guys, I already installed 5.1.1PR to my H950, feels good.
But it seems can only link to tmoblie hpsa (or wcdma?)
But when I used the 5.0.1, I can link to the Tmobile LTE.
May I ask anyone knows how to link to Tmobile LTE by 5.1.1PR?
Thanks a lot~