So I don't have my lift yet and my tires are 285 something R16 10ply but I notice my actual speed differs from my gauge speed. About 10mph at 60mph. So I think I am going 60 and actually I am going 70...waiting for the cop to catch me.

Anyway, how can I fix this difference? Ideas?

 

the speed will be off a certian percentage so its tough to just add an amount. I think you can change the spedo gear that can get you close but its not the most accurate fix. Superlift makes a gadget called truspeed i think, that acts as a programer and will fix it. I think some other programers might be able to fix it as well.

 

I have 35in tires and I bought the Pro Comp power performance tuner which is made by hypertech so its pretty much the same thing but anywho I adjusted my speedo with that and now its dead on.

 

These newer trucks gets it done thru the PCM , so its either go to the dealer or get a hypertech ... the speedo gear thru 94-97 models...

 

I have the 00...was told by dealership that gears ratio means nothing. Can run 3.55 or 4.10 with stock tires.
However if tire size goes over stock 265 then reprogram is necessary for speedo to be accurate.

 

Is changing the spedo gear tough/ expensive? I have a 94 and the same issue.

 

Changing the gear is easy. You just remove the speedo adapter and swap over the gear.
1 bolt 13mm I believe. The gear should be less than $20

 

The hypertech programer will get it done for you also, can run 200-300 ish depending on if you find one used or not.

 

Lets be clear here all. Some years you can do it with just a programmer or parameter change from the dealership. I beleive that is '99 and newer. For all the other years, you need a new speed gear.

 

Where do you find new speed gears. Are there specific ones based on amount of correction you need?