More than likely this is a torque converter issue or simply a fluid issue.
I would suggest starting with checking the fluid level and condition and then change it if it is at all dirty or low.
Here is a guide that will help with this:
https://www.2carpros.com/articles/how-to-service-an-automatic-transmission
Also, here is a guide that will help with transmission issues in general as this may shed some light on what we are seeing with this:
https://www.2carpros.com/articles/automatic-transmission-problems
However, below is a test that we can run through for the torque converter solenoid just to find out if it is functioning. If it is then the clutch itself is slipping and will require replacement.
Please run through all this testing and let us know what you find. Thanks
Images (Click to enlarge)
Jul 22, 2021 at 6:53 PM
