Please, please please don't add other 3rd party plugins that can interfere with the navigation of the TBM and the G1000. We're using the default G1000 base model, but there is a lot of code running inside it, that is also linked to the autopilot. We haven't tested this in any way with the GTN650, and using the GTN can have unpredictable results, along with voiding all support. We can't help people if another developers product is trying to work with ours, and we haven't tested it.
If you want us to diagnose it further, you will need to completely remove all traces of the GTN from the TBM, try the FMC again, and then, if it still doesn't work, send us a log.txt file. Keep in mind, the TBM is still not supported in 11.3. Only 11.26.