If transmission is in gear when coming to a stop the engine shuts off

The fact that shifting to neutral is what is pointing me to my answer. I suspect this is the torque converter.

Normally when the torque converter is applied, it is released when slowing and coming to a stop. However, sometimes the converter fails and is not able to actually release. So when this stays engaged and the vehicle stops moving it stalls the engine because it keeps too much of a load on the engine and it is actually a mechanical connection between the engine and drive-train. Think of a manual transmission that is in gear and when you are coming to a stop and you do not push the clutch in, the engine will stall. Same principal.

Here is the test for the converter. Usually when going through this something will fail the test which gives more proof that this is the converter.

Let me know if you have questions. Thanks