Hi Dean
I have exactly the same problems sinds I got my refreshed GMC AT4 in May this year. I burned my 3 gb in a few days, bought another 1.5 GB and they were gone in a few days. I have been 6 times on the phone with OnStar without results.
I went without Data Plan and I plucked my I-Phone in with a cable. Without doesn’t work!!!! GMC has wireless charging but not when you like to use your I-Phone map. The all new Dodge has wireless!! Using the cable and my phone for an hour drive, including directions I used 13 MB only, that’s normal.
Once more I bought 1.5 GB data 9 days ago and last Friday (August 19, 2022) again 1.5 GB, as of now 544 MB of the last purchase left. I drove a round 1000 km
Last week I used my GMC wifi hotspot and iPhone maps till Friday.
( I turned off all my iPhone background updates)
Friday I turned off my Wifi Hotspot and all Google apps in the settings but in one trip of 1 hour (65km) I still used 170 mb. I made a few other trips on Friday and Saturday with the same results. I was not using maps or any other application. Not Spotify or any.
This morning I only turned on Maps from google (not using directions) and I used 440 MB for 1 hour and 10 minutes 84 km. I left all other google apps off. And even turned my phone off.
I hope GM and OnStar are reading this.
I always drove GMC trucks but now I feel ripped off.
I would not recommend anyone buying a GMC product equipped with this new system.
Best Jan