Your car has went into a fail safe mode, either one because the speedo is not the proper gear ratio for that particular vehicle, not all of them were the same, it depends on the exact model. For instance, a Tarus SE is different from a Tarus LE / SE / on and on, and if the gear ration is not correct, then the TCM will not ssend a signal to the shift solenoids to do their job thus the car wont shift. It sounds to me like your original issue may have been that the speedometer didn't function or work at the cluster, ad you've made repairs to the wrong part. Change your Spped Sensor, and it will be ok, IF the cluster is for that particular vehicle. If it is the proper part, your only issue is the speed sensor.
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