The LTE slider is highlighted to use it. I have turned the phone off and on, I have put it in airplane mode. Is there anything else?
Let's get you connected to 4G! I definitely want you to be able to use the fastest speeds available in your area. Have you checked to confirm you are in a 4G area? What's your zip code?
Try removing the SIM card for a minute. Insert and retest. You can also try this http://vz.to/1n96Ez9. Keep us posted.
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I am still having the same issues after taking the SIM out and also after resetting the Network.