newnewsYes I have also tried this SIM in other phones and they get LTE. I also tried getting a new SIM already. The SIM card is not the issue.
Is this SIM card shows LTE/4G on other phone? Probably you have to go to ATT store and change your SIM card(usually it is free, at least I got for free). Mine shows 4G or 4G+ on ATT SIM card
evnchnI have looked at this website in the past. It appears only one band is missing for LTE, but that not all should be needed.
see if channels of US match with channel accepted by zenfone 6, otherwise no chance of working