Automatic transmission not shifting properly

I suspect we have an issue with a speed sensor which should show up with some codes.

https://www.2carpros.com/articles/checking-a-service-engine-soon-or-check-engine-light-on-or-flashing

If there are no codes in the vehicle then more then likely the torque converter clutch is failing. The way we need to monitor this is with a scan tool so that we can see what the torque converter slip RPM is. Basically this means we need to see how much the converter is slipping. I suspect it will be slipping a lot when this vibration is felt.

Clearly we are going to need a scan tool in order to do this so I understand if you do not have one but if you do, let me know if you have questions on this.

There is one last thing that we need to check. That is the fluid for proper level and condition. If the fluid is ok, then we can try and add an additive that will help soften/condition the clutches in the transmission. It is called friction modifier and available from a lot of different suppliers but I attached a picture of one from Mopar. Any modifier will work but just put one 4 oz bottle in the transmission and then drive the vehicle for at least 500 miles to all it to work in and the issue should be getting better if not go away. If it does not effect it then it could still be the converter clutch but it is just too far damaged.

Let me know if you have questions on this. Thanks