I have slightly modified the core data model on my app( could of new fields and an attribute constraint changed). CloudKit syncing works fine when all devices are using TestFlight version, but now the App is in production, and installed on devices, Cloud syncing not working. Do I need to move the revised app to production, or can someone point me to where I put the Core Data Model into production so that I can figure out if/how to get new version to production? I gather TestFlight versions use the development version, but production using production version.

You have to deploy the new schema to production via your iCloud console and you have to publish the new version of the app to the App Store. The old apps don't know the new version of your model.