Hi,
Based on the speed you are traveling; it is normal for the transmission to downshift. However, the light shouldn't be on.
As far as possible issues, since the check engine light is staying on, there will be diagnostic trouble codes stored. We need to know what they are.
Here is a link that explains how to retrieve codes:
https://www.2carpros.com/articles/can-scan-controller-area-network-easy
If you don't have a scanner, take it to a parts store and let them scan for codes. Most do it free of charge.
Do this and let me know the results.
Take care,
Joe
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Friday, March 24th, 2023 AT 10:33 PM