My iPhone 5 won't receive LTE speeds?

Okay, so my iPhone 5 is factory unlocked for T-Mobile running on IOS 6.1.2 and I'm currently on vacation in New Mexico and have been getting only Edge speeds. This is about 40kbps and it is honestly quite worthless. In Missouri, I would easily receive LTE speeds which was about 1.3Mbps but for some reason it won't connect down here? I have my APN settings altered (not sure if they're are right, though). I have no idea what to do and I know it's not a signal problem because I have 5 bars down here. In Missouri, I only had 3-4 but it was still faster. This is only quite a pain and I'm wishing for a fix. Anyone have any ideas?

Added (1). My sister has an Android phone and we have the same exact plan. She has 4G speeds at all times while I suffer with Edge. Why?

Added (2). @Robert Mendez: then why can't I get at least 4G like my sister's phone does? 4G's still 20x faster than Edge.

The data coverage is most likely poor over there for LTE

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