In the Custom Options menu, you should find a "Gear Ratio" selection. If you click on that, you may or may not see your correct GR. In my truck, it is the installed gears 3.73:1, but others have found different results.
If your speedo is nearly correct now, your GR is probably a valid number, but if it is badly inaccurate, you will likeky need to set it manually. You can find your axle code on the VIN sticker on the driver's door. Here is how you interpret what you see:
19 = 3.55 open
H9 = 3.55 LSD
26 = 3.73 open
B6 = 3.73 LSD
27 = 3.31 open
18 = 3.08 open
25 = 4.10 open
B5 = 4.10 LSD
Again, if you reopen the Custom Options menu, remember to "Load Previous Settings" as the
first step.
- Jack