I have the AT-778UV. Maybe my setup can help? The MIDX23-50 channels are Midlands extra channels. There's a ton of videos on YouTube that are incorrect with channel spacing. FCC ruled out wide band (25khz) on GMRS. You can reference my code plug data from website below.
https://wiki.radioreference.com/index.php/FRS/GMRS_combined_channel_chart