I went and pulled an overhead display off a 98 blazer for my 02. It is one of the displays that has temp/comp but also mpg and all that jazz. My blazer didn't come with an overhead display so I put it all in myself.
I have the harness, display, and the mounting bracket. I wired it all in myself thanks to many posts on here for guidelines.

Here's where I'm stuck...
I already have power and everything. I have the wire already ran to the OBD II and that just tells me my range and how many gallons I've used or whatever. I tried to hook up the wire for the VSS today, I couldn't find where to mount it under the hood so I direct wired it to the plug on the transmission (purple wire) like everyone said on here, it was all working fine and dandy (on the overhead display) except it wouldn't shift out of 1st gear and my speedo didn't work, and my average speed on my overhead display was reading 136mph..

Where should I connect the VSS wire to?

 

You might be able to get it in the radio harness. Upper model radios have a system that increase the volume of the radio as the vehicle speed increase, and had a VSS signal in the radio harness. I believe that it's the same purple colour as on the transmission.

 

Thank you so much! I'll pull the dash apart tonight and see what I can come up with.