all that would possibly do is cause a firm delayed upshift. absolutely nothing related to the shutter. Nice thinking but not your problem. it even could be that the sensor is unplugged you can measure the sensor with a DVOM in Ohms and come up with the validity of sensor output and you would have a MIL with a code

 

Welp, it's fixed. It was the ambient air temp sensor.
The sensor was removed right before I got it and over the course of 500 miles the problem presented itself and slowly but consistently got worse. I replaced the sensor and the problem quickly faded away over about 100 miles and now the transmission feels great. I guess it was learning incorrect shift data because it always thought it was -40 F. It's also nice to see the outside temp readout.

 

had you stated the outside temp reading was false, that would have directed to the problem a lot sooner. but a shutter is definitely not related to that sensor. It can cause change in shift point which may seem like a shutter. but at least you got it fixed. now you see the problem of speculative guessing on the internet. there are some things that are just a commonly known problem however when something needs diagnosis, not having the knowledge, skills or tools, it's a total shot in the dark.. thats why sooooo many people just throw random parts at a problem. all that does is cost time, money and aggrivation. Then one asks (demands) a solution to the problem...and when they don't get the exact answer, a hissy fit ensues.