99 SLT 4x4 5.2L

Is there a way to correct the speedometer reading if you have larger tires than the original build?
Is there a different output speed gear for the speedo cable?
Currently have 31x10.5 R15 installed, which matches my VIN print out, but the door pillar sticker says P215/75R15.
I used a tire conversion chart online and it confirmed that the difference I see on my dash is because I have the 31's installed.

 

There is no speedometer cable. The speedometer is electronic. It's read from the speed sensors.
A DRBIII, old dealer item, can update the computer.

 

Most of the big chain tire stores should have the ability as well.

 

Thanks guys I will ask around.