I've already posted on chevytalk and am not getting a response.
I hav an '88 s10 blazer 4.3L 4x4 which is giving me a VSS code. Now usually for this year the sensor is located near the tailshaft of the transfercase/tranny. But I heard on the 4x4s they are under the dash near the guage cluster. Is anyone positive where it is located?

The actually pickup sensor is on the tailshaft housing on the transfer case. The name of the box you're thinking of escapes my mind at the moment. But a quick check on the sensor, should have somewhere in the neighborhood of 800 to 1200 ohms resistance. Should produce atleast 100mV spinning the driveshaft.