I've been doing this long enough to know that three opinions don't necessarily equal one answer.
When a dealership says it's the transmission, the transmission shop says it's electrical, and the electrical shop says it's the transmission, I don't vote. I go looking for evidence.
The vehicle doesn't care what any of us think.
It only responds to physics, hydraulics, and electricity.
So I start asking questions like:
What can we prove?
What tests have actually been performed?
What evidence points to the transmission?
What evidence points away from it?
I've had vehicles towed in that supposedly "needed a transmission," and the problem turned out to be a bad ground or a failing ignition switch.
I've also seen the opposite. Everything looked like an electrical issue until pressure testing and scan data proved there was an internal transmission failure.
One thing I've learned over the years is this:
Opinions don't fix vehicles. Evidence does.
That's why I don't worry about who was right or wrong before it got to my shop. I worry about what the vehicle is telling me today.
Sometimes the dealership is right.
Sometimes the transmission shop is right.
Sometimes the electrical shop is right.
And sometimes...they're all chasing the same symptom instead of finding the cause.
That's why the first thing I try to diagnose isn't the transmission or the electrical system.
I diagnose the failure.
Once you understand the failure, the repair usually becomes obvious. That's how you break the tie.