[Q] sm-t850 wont connect to any US LTE topic

i have an sm-t850 from HK. I'm trying to get it to connect to any of the US LTE carriers with no luck. I have rooted, changed ROMs, applied a regional unlock app and comfirmed that etc. No luck. I have access to some LTE radio logs and can see that on a band 7 LTE radio the device will begin authentication, pass authentication but will not accept the 'authentication complete' message. Is there anything that I'm missing as far as firmware locks (regional lock has supposedly been removed and verified) or anything else that would be stopping the completion of authentication?

Does anyone know of any way to get a complete build sheet on this device via the IMEI?

TIA, Jeff