Figure out what gears are in your diffs. 35's and 3.55 gears don't go well together.

 

possibly I replaced rear speed sensor and wiring cuz I actually lost the speedo and it was stalling coming to stops. So I replaced it, couldn’t clear code with my snap on scanner because it doesn’t recognize the odb2 port, another issue I’ve never figured out…..but I disconnected battery for 24 hours, engine lights been off (and yes it comes on when I cycle key) but when I do the key dance trick my display says “p0500” then “done”….so I haven’t continued diagnosis cuz it all works

 

This is a 97 truck?

If that's the case, there are a couple sensors on the trans, output speed sensor, which the PCM uses to make sure the trans is doing the right things, and the vehicle speed sensor, which is in the tailshaft of the trans, or t-case, depending on how many drive wheels you have..... The sensor on the top of the rear diff is the rear wheel speed sensor, and is only really used for ABS function.

If I remember right, on the 97, the VSS gets it 5 volt signal from the PCM, the return signal actually splits, one going to the speedo, the other going to the PCM...... It is entirely possible for the speedo to work just fine, but, the PCM still doesn't get it's vehicle speed signal.... Can only verify that with a scanner that can read live data.

 

I've noticed that it'll shift immediately after I let off the gas each time, so what does that mean?

 

Likely a separate problem......