FWIW, i just did a long return drive from for almost the entire length of Interstate 5 on the West Coast of North America, Los Angeles to Vancouver BC, using my T Mobile sim card.
i have never been able to rely on my Pro 1x, so left it in a drawer and used another phone with LTE Discovery running and logging.
The following bands are the full scope of LTE bands that my 1x would have had access to, anywhere along the Interstate 5 corridor: bands 2, 4 (also 4 roaming on Telus in Canada), 12, 17, 66, and 71.
The 1x specifications page does not list band 66 or 71 as available, but b