Have you actually tested the torque sensor on an oscilloscope or just replaced with unknown scrapyard part?
the RX8 steering torque sensor was updated by mazda later on. The system also reports torque sensor faults if the system voltage drops below 13V while running, usually a sign of either a bad alternator or a dumb ecu (alternator is controlled by ECU in mazda). It will also throw stupid codes like this torque sensor if the can bus goes down momentarily, check the hi and lo can line voltages and make sure that they are stable at 2.3~2.5 V - if not then you have a can bus problem - and you will have other can bus error codes also.