Speedometer misreading

What's up, so I bought a 2004 cobra with 21k miles on it 6 months ago. Previous owner beat it to shit so I'm finding new issues all the time. The newest problem is my speedo reads 5 mph faster than what I'm actually going up to 45mph. After 45, it compounds. Example 70 on my dash is 63 on GPS. Previous owner put 3.73 gears in. But the speed sensor is located on the transmission, is the gearing causing my difference in accuracy? How can I remedy it? Thanks for the help

Yes, the shorter gears are what's causing it. It would need to be adjusted with a handheld tuner that is set up to allow you that capability.

Thank you so much for the reply. I have an hp tune but no handheld. I'll do some searching for a handheld

If you can access the HP Tune you should be able to adjust the speedo that way.

Maybe it's just me but I've noticed even on stock gears the speedo is off 3mph or so anyone else notice this