Ok, 91 Z28 350, th350 trans swapped in with stock 700r4 tailshaft (I didn't do it, so I'm going by what I see). Speedo reads almost exactly 1/2 what it should (i.e. 40mph when you're going 80). It was verified using a scanner that the computer is outputting the same erroneous signal, so it's really some kind of VSS issue. Hoping someone here has an idea about how to fix this problem!

Nobody has an idea? I'm thinking VSS, but don't know exactly why it would be giving me this odd reading, anybody know what the output signal should be?

The gauges in these cars are ridiculous! I've got a tach that reads way too high (gonna try the resistor fix), a temp gauge that is about 40 deg low, and a speedo that reads 1/2 what it should that I can't even see at night cause the bulbs burned out. Sheesh! Not to mention I don't think my engine puts out 60+ psi oil pressure all the time. I'm about to throw the whole dang dash in the dumpster!

Sounds like you have a 2000 pulse VSS. You need a 4000 pulse VSS in a 90-92 thirdgen.

Finally, something that makes sense! I don't mind changing out parts, but I hate just throwing crap at the wall and seeing what sticks. I wasn't aware that there were two separate VSS's, I'll swap it out and see. My buddy who owned the car before me swears that it worked when he had it, but after 3 years of letting it sit I think his memory might have faded some. Thanks Kevin91Z!