What leads you to say it's not been changed? (rear end)

 

Well a couple things do but for starters, changing the ratio in forscan and with the hypertech also yielded no results on the speedometer. It doesn't appear that the stock rear case has ever been cracked open either. I will raise raise truck tonight to verify for certain but without the tuners being able to affect rear ratio, I'm still dead in the water with the speedo

 

I raised and locked the rear to verify 3.55 rear end. It is the same as the door jamb. Pretty much out of ideas on what to do. Could the bcm not be talking to the speedometer or pcm?

 

I think you can test this by attaching Forscan and running the speed PIDs while you drive. See if the computer agrees with the speedo. Should help narrow it down to a sensor, the PCM, or the cluster.

 

That's a good idea because a discrepancy could point to the cluster having an issue.

Does anyone know if the speedo pulls its speedo data from the bcm or pcm? I could pull some wiring diagrams to verify if needed.