Speedometer bounces while driving

link with some info about faulty speedometer.
https://wheelzine.com/speedometer-not-working-properly

https://maxima.org/forums/4th-generation-maxima-1995-1999/311797-fixing-speedometer-odometer-work-sporadically.html

This may not be of any help but I had a 94 and the speedometer kept messing up. One day my wife was in it and she was stopped at a red light and it was bouncing around 30 MPH. She took it to the dealer we bought it from. They told me it is run off electrical signal and the alternator was bad. They changed the alternator and we never had the problem again. Just a thought check your alternator see if voltage is good are bouncing around. You can check it at the battery while it is running. I have never heard of anyone else where the alternator effected the speedometer but it is what I was told and they did change the alternator.
I will say I do not remember the MPH being 0 while running.

Either the speedo cable or the plastic gear in the tranny.

It won't be a cable, as it's impossible for a cable driven speedo to perform this way.
It's an electronic speedo.

Check and/or replace the speedo sensor in the gearbox housing.

Sounds like you need a new accelerator cable

This is your speed sensor. Now i do not know if this is going to be cable driven or electrical because they used both in 95. Your local auto parts store will tell you exactly what kind is in your truck. I just changed one friday on a 94 ford escort and it was electrical. The part was around 20 dollars for the speed sensor.

sounds like you may have a problem with your speed o gear in trans.

you probably need to replace the cable or the speedo

the speedo cable needs to be replaced,they wear out internally and start to jump arounr inside the sheathing

most certainly a speed sensor problem!
it may not be pulsing properly or the drive gear is worn etc etc.
Cheers Rob

replace speed sensor