Does not shift or slip is my transmission bad?

Hello,

Any time there is shifting issue first item needs to be checked is the fluid.
Low or contaminated fluid can prevent the transmission from shifting.
If there is not enough fluid, the transmission will not have adequate fluid pressure to perform the shift.

Another item could be a faulty shift solenoid.
Over time with wear and tear the solenoid can malfunction and will not function properly, which can lead to shifting issues.

The shift solenoids are located inside the transmission. To access them you will have to remove the transmission pan.

Here is a helpful article:

https://www.2carpros.com/articles/automatic-transmission-problems

I have attached diagrams for your reference.

Please let me know if you have any questions.
Thank you.