LTE settings

Are there any particular settings in the 4th gen iPad that are required to access Telstra's LTE network? I used to get LTE on this iPad at his location, but after a trip to the US and using an AT & T SIM card there, since returning and putting my Telstra sim back in, I can't seem to access LTE any longer. Could the AT & T network have change some setting in the iPad?

Obviously LTE is switched on in settings.