Default [Q] Sprint HTC One M7 unlocked to T mobile issues

Hello All. This is my first post to this forum. I have recently unlocked my old M7 to T mobile for a friend. I was able to follow many guides from theses forums and get the set up working. I am currently running into an issue tho. Randomly is seems that the GSM network will get disconnected. The only was to resolve this is to reboot the device. When I reboot it is have to enter in the secret code and select the preferred radio mode again and re-register to the T mobile network. I was wondering if anyone knew of a way to fix this. Also if anyone could tell me if it is at all possible to flash a T mobile ROM to this device now that it is unlocked? Many thanks to any helpful answers.