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I would be very cautious about regearing the final drive on a tC or adding a ratio. Either will upset the On Board Diagnostics (OBDII) because the diagnostics are expecting certain values for speed vs. rpm. If you change them without changing the ECM's programming, you could have a constant Malfunction Indicator Lamp (MIL) glowing to remind you it is unhappy.
Adding a gear to an existing transmission is next to impossible unless there is a clever way to do this with software manipulating an overdrive component (Toyco did this with the A340E in a Lexus model to make a 4 speed a 5 speed). Again this would be a mod to the ECM, not the gearbox.
I seriously doubt you'll have anyone say, "Yeah, we can do that" with any truth in the statement.
Adding a gear to an existing transmission is next to impossible unless there is a clever way to do this with software manipulating an overdrive component (Toyco did this with the A340E in a Lexus model to make a 4 speed a 5 speed). Again this would be a mod to the ECM, not the gearbox.
I seriously doubt you'll have anyone say, "Yeah, we can do that" with any truth in the statement.