Speedometer calibration for 99 Silverado

[robd0gg]

I've done some searching and not found anything recent, (just some really old threads here).. but I have a 99 1500 with 20in wheels, and P275/60R20 tires. The previous owner told me the axle ratio is 3.73 which matches the RPO code in the glovebox. My speedo consistently displays a speed about 8-10% higher then what my GPS shows, which is strange because with larger diameter tires, I would think the GPS to read higher then the truck speedo.. oh, and the transmission was replaced about five months ago.

 

I am unclear from searching, what my options are for correcting this. I've read of some DIY repairs one can make to the PCB? but not willing to go there.. is this something a dealer can fix with a 99? and I know there are tuners available for this as well.. would something like the DiabloSport Predator Flash Programmer be a good option?

 

thanks for the knowledge.

[Bob D]

Welcome, Robt.

Dealer should be able to handle it.

An alternative to DiabloSport Predator is hypertech.com/products-comparison.aspx

May want to call the dealer and let your wallet make the decision.

[govener71]

Superchipsu programmers, 2815, for your truck are going for a little more than 100 dollars on eBay. I just bought one for correcting my speedometer. Had one for my last truck then stupidly sold it.