Just had a trip through Maine up to Canada, and noticed something .. unusual.
T-Mobile devices (SIM) ‘prefer’ AT&T LTE (throttled to ~256kbps) over US Cellular 5G/LTE - throttled to ~3Mbps.
While ‘service is service’, I do find it strange to have T-Mobile preferring AT&T over US Cellular. US Cellular can still be manually selected, but by default, AT&T’s service is … less functional due to the heavy throttling.