Misfire in 3rd gear

Hi everyone my 3ltr auto SC has developed a misfire, it occurs in 3rd gear without overdrive when accelerating from low speed and reaching 40/50 mph it will misfire, it has now become quite predictable and stops as soon as overdrive is engaged even if throttle pedal is not moved, so I suspect a gearbox sensor rather than a throttle position sensor ( I have a new TPS to fit if kneaded ) . Has anyone had this problem and found a solution.

Are there any gearbox sensors?

I thought it was just a speed sensor and the rest was solenoid drives for the gearbox.

The gearbox has it's own ECU that talks to the engine ECU. I can't imagine it talks much, but maybe dips the power when the autobox ECU decides to change gear.

If so perhaps the gearbox ECU caps are failing and it keeps telling the engine to reduce power. I've not taken mine apart - but it does live under the selector. Careful, they seem to be as rare as engine ECUs.

There should be only 1-2 wires between them, I did post up some engine ECU diagrams (for the 1kz in a hilux or something) that matched. The idea would be to find the wires and monitor the voltage (with a 12V LED or something) and see if it behaves.

Its not a problem at the moment so inclined to just keep an eye on it.