I don't know much about Cossies, their electronics and fitting/setting up the sensors. But as the ECU still has problems with the engine speed sensors this is the first thing to check. TDP = top dead point, so this is the crank position sensor.

Probably it's just one sensors that doesn't work as it should. The ECU gets signals that don't match and has error codes for both. Easiest things to do: check all connections. Plug the ECU off and back in again, do the same with the connectors for your sensors, check for rust/oxidation/dirt on the contacts and check all the mass connections to the body at the battery, inside the car and in the engine bay.

And having someone with an oscilloscope to check the sensors might be helpful.