Okay, now I am really confused.

NP8 is the NVG236 transfer case.

I have the 1999 Blazer service manuals on my lap right now. On Page 4-252, I see the wiring diagram for the NVG 236 transfer case.

In the wiring diagram you posted here, same drawing (TransferCase_connectors_2.gif), I see that (3) is the VSS on the passenger's side, and (4) is the "Transfer Case Rear Propshaft Speed Sensor and Connector" on the driver's side.

In my manual--same drawing--those are switched. (3) is still on the passenger side, but now it is the rear propshaft speed sensor, and (4) is the VSS sensor on the driver's side.

I changed the one on the passenger side. Did I replace the wrong one?

It looks like they are the same sensor and take the same connector.

 

Just got back from the dealer. Got ripped off price-wise, but the correct part number for the VSS plug is GM# 88987993, other part numbers are PT1978 (Delco) or TX3A (Standard Motor Products)

This is a plug with leads already attached. I paid $52 at the dealer, they seem to run about $25-$28 for the Delco part, $10-$13 for aftermarket.

I paid the full price because I could not be sure of the part # until I bought one...