99 alero 3.4 bouncing speedometer

Ok so here's my problem

I have a 99 old alero 3.4 6clyndr
When I start the car it's turns on fine and idles ok
When the driving begins is where the problem begins
The speedometer sometimes will stay stuck in 0mph
While I'm driving
After about a minute or so the needle on the speedometer begins to bounce up and down in between 0mph n how fast I'm actually going
From there this has only happened twice since the problem began on Thursday of last week the rpm will go up high and the car won't accelerate
But goes back to just the bouncing needle and Car doesn't run as smooth
I've done
Tune up
New alternator
New serpatine belt
New o2 sensors both of them
New air temp sensor
New maf sensor
New intake manifold with new gaskets
New egr system
New speed sensor
New catylictic converter
New fuel pump and filter
New air filter
New oil filter
Replaced coil packs
New cam shaft sensor....

You replaced the transmission output speed sensor?

Basically, you need a scan tool to read data from that speed sensor...if the data is ok, but the speedometer isn't, possible cluster or PCM.....

If data is bad, then you could have a wiring problem from the speed sensor....

You also need to scan for codes, all codes, not just P codes....

I tried getting my codes read at AutoZone today but couldn't because they said my service engine light wasn't on therefor it wouldn't read any codes
I did research on my own and found out that it could be the output speed sensor as you mentioned
But I can't find where it's located

Many chain stores will have code readers, but not bidirectional scanners. You need a scanner to be able to read live data.

The VSS is located on top of the output/differential housing on a 4T60/65 transmission.