google is your friend. There's a known glitch that causes the 3g to lte handoff not to work properly with that device
When you move into an LTE coverage area from a CDMA coverage area, it may take up to 2 minutes of the device being in idle mode before it changes to LTE coverage. There is a temporary workaround, remove and re-insert the device. The known issue will be corrected in the first Maintenance Release (MR1) of software for this device.