Sounds like you are back to the beginning of this saga.

Red_2005_convertible is !00% correct: "the ignition trim ring you mention is the antenna for the SKREEM key transponder reader, so if you didn't have that plugged in, the car would definitely not start"

You check transmission fluid level with the car running in park and warmed up. So look at your temperature gauge and when it is about half way, which is normal operating temperature, then check the fluid level car running in park. Should be midway on the dipstick. If you just stick the dipstick in the tube cold the fluid will be high up out of range.

First post P0715. That is in the service manual; at this point probably the conductor plate speed sensor (That should throw a code) assuming your new SLA is communicating properly to the transmission.

The "car drops idle" as it warms up. At first start the car is cold and should idle about 1200 RPM (it is winter) after a minute or so it will drop down a little and then again when the thermostat opens it will drop down again to normal idle speed.

With the car not moving at all it may be that you still have a wire disconnected somewhere. If you can probe the wires with everything connected check voltages at the TCU on the wires going and coming from the transmission. If you have power there then it points to the conductor plate being the problem.