Okay then I bet you have a bad wire somewhere in the harness

 

Well F16's have a 25,000 page book of troubleshooting steps, written so a 6th grader can read it effectively

Its not a PCM issue, the PCM is seeing speed, is outputting speed, you can read speed on the scanner, the truck is shifting (which, surprise! is all mph based). We can eliminate the PCM, VSS and everything in between

What can be the issue is the instrument panel driver, if the truck has one (unsure of myself), or a break in the harness between PCM and cluster. We can't diag that over the internet. If you can work on planes, you can figure out whether or not the speed signal from PCM to cluster is valid

That line might multiplex, so you might need an o-scope for proper diag. I do not have a 99-02 FSM, but that might also be a place to start

https://lt1swap.com/99-02_vortec_pcm.htm

Pin 50, red connector. Output is a sine wave. For $100/hr I'll come do the real work for you too

https://ls1tech.com/forums/generatio...utput-pcm.html