I have a 1994 Firebird that has the 4L60-E Automatic Trasnmission.

On the same day my transmission quit shifting, my speedometer also quit working. All the transmission people tell me I need to re-build my transmission.

I am not buying that the ELECTRONIC transmission that relies on the car speed to shift and the speedometer both going out at the same time being independent problems.

I suspect it is the PCM or the speed sending unit. I do not know exactly how the PCM gets speed information used to shift. Does this input come from the transmission, How can I see if the PCM is getting car speed