Hello, If you have already replaced the ECU and the Throttle Body without any vacuum leaks, you are likely looking in the wrong place. On manual transmission cars like the Lacetti, the most common cause of RPM flaring (or rev hang) when shifting gears is a faulty Clutch Pedal Position Switch. When you press the clutch to shift, the engine loses its mechanical load. If the clutch switch is broken or disconnected, the ECU does not know you are shifting. It fails to cut the fuel in time, causing the RPM to suddenly spike by about 500 RPM. Connect your scanner, go to Live Data, and check if the state of the Clutch Switch changes from OFF to ON when you press the pedal. Good luck!