A flashing TCIL (Transmission Control Indicator Lamp) accompanied by DTCS P0791 and/or P0794 and harsh transmission operation may be caused by a malfunctioning ISS (intermediateShaft Speed) sensor. Use WDS VDR or Data Logger and record: GEAR, ISS_SRC, RPM, TR and VSS while driving the vehicle. Graph the recorded data and look for an erratic/noisy ISS signal. Compare the recorded ISS signal to the "Normal" and "Abnormal" images below.