Hi,
First, is the transmission fluid clean and full? If you haven't checked, follow the directions below and let me know the results. (See pics 1-4)
Transmissions depend on what is called line pressure and shift solenoids to function. What you described at first sounded like a pressure issue, but I need to know if this is the only shift it happens during.
As far as testing, what really should be done is this. First, scan the can-bus system. CAN stands for controller area network. Basically, all computers/modules are tied together via a few wires. With this type of scan, trouble codes can be retrieved regardless of the module storing them. Here is a quick video showing how it's done:
https://youtu.be/InIlnsjOVFA
The other way to test for a harsh upshift is by driving the vehicle with a live data scanner and watching shift commands from the PCM/TCM (power/transmission control module).
I realize these are things that may be difficult for you to do, so let me know what I can do to help. Also, here is a link you may find of interest:
https://www.2carpros.com/articles/automatic-transmission-problems
Let me know what you find or if you have other questions.
Take care,
Joe
See pics below.
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Wednesday, November 17th, 2021 AT 8:20 PM