Speedometer way far off with shift points

A different differential will cause the speed reading to alter and will larger tyres, have these been changed?

The tires are the stock size and so is the diff. I'm starting to think that it's an electrical issue, but I don't know how to check this and I can't find a wiring diagram for this anywhere online.

Hey,

The speedometer has a microprocessor that goes bad in the cluster which feeds info to the transmission. I would try replacing the cluster first, here is a wiring diagram to show the cluster wiring

Please let us know what you find so it will help others.

Best, Ken

Hi Ken,
actually a friend of mine has the same truck and he let me switch gauge clusters with his to see if it would change anything and it didn't.

Okay, here is the wiring for the VSS is goes into the BCM so it's either bad or there is a bad connection somewhere causing high resistance in which case you will need to do a pin to pin check here is a guide to help you.

https://www.2carpros.com/articles/how-to-check-wiring

Let me know hat you find

Best, Ken

It's definently not a bad vss sensor as i've tried 3 different ones and none have changed anything. I'll look into the wiring link you gave. Also, do you know where I could find the wiring diagram for the electric 4x4 actuator motor?

Yep I saw that, I meant the BCM was bad, here is the rest of the wiring you needed, let me know what you find out.

Best, Ken

Just to add to this one have you checked to see what the scan tool reads for speed compared to the speedometer?

Good call

Okay, so I've done some testing and learned some stuff. I used my obd 2 reader to check the speed and it corresponded to the gauge cluster so it's definitely an issue at the pcm or before it. Also I tested the 2 wires in the vss plug for ohms like you said above and they both came back with about.5 ohms so they should be fine. If these wires are fine then doesn't that only leave the pcm to be at fault? Or is there something I'm forgetting?

Its sounds like you got everything and the PCM is the fault. It happens, please let us know if that fixes it so it will help others

Best, Ken

Got my new pcm in. Swapped it all out and nothing changed. What a bummer. Any idea on what I can do next?

It sounds like you have high resistance or a bad ground in a wire somewhere, please use wring diagrams and recheck the system doing a pin to pin check again, we are missing something.

So one thing I've noticed from driving is that once started it doesn't read any speed for a few second. Then it says trans fault and gives a bunch of alerts. It gives these same alerts when there the speed sensor is unplugged. After driving for 30 seconds it recognizes the speed sensor and shoots up to like 80 mph. I don't know what this tells me.

Are there any codes being set from all the warning lights coming on?

Yeah. It throws codes p2106 and p720.

Still haven't found a solution. Does anyone know if the abs speed sensor in the front wheels could affect the speedo?