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You must get a scan tool hooked up which can read and show the stored transmission codes. There are about 60 different codes all meaning something different. I would need to know which shift or which gear is harsh or delayed or slipping to help pinpoint the concern not knowing the codes. Anytime the OD light flashes the computer is going to boost the line pressure to max to try and save the transmission till you get it to a shop to prevent more damage from normal pressure with a damaged clutch.
If the OD light is flashing then this still means there are trans codes and apparently the tool your using does not have transmission capability.
P0605 means there is a internal PCM read only memory error. This is a common code if your using a programmer or chip. If your not then you need to have your local dealership reprogram the PCM and if the code returns a new PCM is needed.