I just got a GPS and the speedo is 3 mph above the GPS regardless of speed. That is, if the speedo says 13, gps says 10, if the speedo says 83, gps says 80.

Is there any way to fix this, such as by opening up the speedo and adjusting the needle, or something else?

 

If you're running bigger tires that'll do it. Change the speedo gear to one with the right amount of teeth for your gear ratio & tire size.

 

Tire size difference would give you a percentage error, not the same error all the way across the board. Just know that your speedo is off, and drive accordingly, don't think there is anything you can do about it.

 

Yeah I already have the correct gear in there for the tires and axle ratio, it'd be spot on if not for the 3 mph. It would be nice if I could pull off the needle and put it back on at a slightly different angle.

just curious, I understand these trucks don't use a speedo cable, so how does the speedo work in the 95, is there a motor or something that makes it work, is it PCM controlled, or what?

 

The gears drives a signal generator at the trans. (VSS) That signal goes to the PCM, and the cluster. Speedo shuffles the needle around by that signal. You *could* take the needle off, and reposition it though...... I think. Just be careful.

 

+1
I did this to a Taurus once, I actually drove it with the lens off and needle in hand and found a straight road and put the needle on while driving.. a bit tricky but after that all was good.

*Do at your own risk