[D13]

Depending on which 88 (NBS = pickup) you got it from the trans may supply pulses to the ECM which then filters it to run the speedo. The other version (OBS = burb/blazer) uses cable drive speedo with a VSS output box hung on it. Either way you need the appropriate input. Old style uses 4000 pulse per mile and the new one uses like a 132,000 signal divided and dropped down for various systems. There were a couple years of crossovers where Burbs has cable drive trans rather than electronic outputs. Need to make sure your trans/dash/ecm all play together.