Here's how I got it back to 4G (LTE):
- Connect to your MiFi
- Log in to your MiFi by typing this URL into your browser: http://192.168.1.1/
- Click on "Setup Wizard"
- The default password is "admin" (unless you've changed it)
- When it asks you to set up a new password, click "cancel"
- Now you'll see that you have several new menu options at the top red horizontal navigation bar: Home, Wi-Fi, LAN, WWAN, Security, Advanced
Now, you'll want to click on WWAN -> and then go to the "WWAN Settings" at the bottom of the page.
- Under the WWAN Preferred Mode, select "LTE only"
- Then, click "apply" and the device will reboot.
My understanding is that this is a temporary fix. Therefore, you may need to do this periodically if you move into areas where you only have 3G coverage. The MiFi could have a tendency to get "stuck" in 3G mode and it needs to manually get moved back to 4G using the steps outlined above.