To be clear, I went with aftermarket gauges, so I don't have the experience, but I did use a Dakota Digital DSL-1 to get the right tach on my new gauge set. Not sure if this would do it for you all that kept the OEM gauges coming from the PCM.Seeing as a Speedo healer or yellow box does nothing but change the input squarewave frequency , might that also be used to change your pulse rate to give the pcm what it wants .?