Accuracy speed readout

I have a digital dash ( Casper upgraded chip) display and while test driving I notice speed reading is about 12 miles faster then the GPS reading. Is it possible the VSS Buffer Module needs to be replace?
Thanks

What does the scanmaster say

Scanmaster reads the same as the dash display.

What sized tires?

Right now 15" stock rims, Do you think if I replace with 16" I would see the display reading correct speed displacement?

What size tires not the rims. Are they low profile? Overall height which throws off the number of revolutions over a given distance because of the circumference.

My correction, stock rims with 215/65-15 tires, In the future will replace with (rear) 255/50-16 tires (front) 245/50-16

Stock 3:42 rear gear?

Yes Stock 3:42 rear gear

Change the speedo gear in the transmission

I believe there are several types of speedo gear for tranny. How do you know besides the color which is the correct one ?

As to the 1st thread, Is it possible the VSS Buffer Module needs to be replace?