There is a Target in zip code 27617 that I frequent. The entire region around the store has wildly fluctuating signal strength -- from solid LTE to roaming at any given time. This makes it pretty frustrating to be a T-Mobile customer when I'm in the shopping center.
T-Mobile does not have a 700 MHz in the Raleigh market. This creates some issues with dead spots. T-Mobile's new 600 MHz licenses will do much to improve the situation but it will be about a year from now before TV stations have cleared the spectrum so that T-Mobile can use it. It will also require a new phone.