Hi fellow Metro user here.
I'll assume this is a Metro-branded phone.
It depends on the tower you are connected to at any given time. You may see 4GLTE or just 4G depending on which service is available from that tower or has the strongest signal. Also not all Metro/T-Mobile service areas have LTE yet, although most major cities do there may still be some places that have only 4G (which is technically HSPA 3G but is called 4G by them).
So as you move around and connect to different towers you will likely see the indication go back and forth between the two. If you get far enough into the boonies you might even see an "E" for 1x Edge service.
Finally there is a setting in the phone that selects what type of networks it will connect to, but since I'm sure you haven't messed with that it should be on the default setting which allows all types and automatically selects the best available.
Short answer, don't worry about it. The 4G service is still plenty fast.
