This sounds like an issue in the valve-body. The shift solenoid are inside the valve body that control each shift and a separate solenoid for overdrive.
I attached the process on how to replace this. I would suggest taking the valve body apart and inspecting it but the solenoids are only around $20.00 so I would just replace that and then put the valve body back together.
The solenoids control where the fluid pressure goes to determine what shift will happen. If the solenoid has failed it will not shift. However, your vehicle has one solenoid with two coils inside. So you would need to test each separately but with this being such a common unit, the components are pretty cheap so I would just go ahead and replace it.
Please reach out with questions. Thanks
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Wednesday, March 24th, 2021 AT 1:42 PM