I created a map of the current live LTE coverage in the McKinney area for you. See below:
Drive to be near one of these towers. Change you phone from CDMA/LTE mode, to CDMA only mode. Leave it there for a minute or two, then switch it back to CDMA/LTE mode. If it finds a 4G signal, then good. If not, there may be a problem with your device.
We have had a few members confirm they are receiving LTE signals from these sites around McKinney. However, go to more than one to rule out the possibility that one of the sites was temporarily down.
Let me know what you discover. Hope it works out for you.
Robert