Hello,
I don't think that the transmission is toast. In the diagrams down below I have included the factory diagnostic troubleshooting guide for DTC P0731. It will help you pinpoint the problem so you can get it fixed, right, the first time. Please go through this guide and get back to us with what you are able to find out.
Thanks,
Alex
2CarPros
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Sunday, June 16th, 2019 AT 1:44 AM