I just got the sim for the Tech Connect+ At&t plan and tossed the Moxie junk in a box. Hooked up a top of the line MOFI5500-5GXeLTE-EM9191 with a CAT 20 LTE modem and 5G support and got the sim activated. First boot it does 12Mb down and 12Mb up. Ok so I do selective bandlocking and disable the bands with low connection strength. Same speeds.
Next I hop in my truck and run the router off a solar generator and drive 40 miles looking for towers. 12Mb down and 12Mb up no matter where I go even 50ft next to a tower. I even drove to a tower in a college parking lot, the speed will surge to 50Mb then immediately drop to 12Mb.
At&t is throttling the speed on this plan, it doesn't matter how good your device is.