Is there a way to find out what gear ratio my truck's diff has? I know I could call a dealer with the VIN but I was wondering if there was any other way.

Give you a clue... I've got 3.55 gears...

You can look in the glove box and find the axle ratio on the information sheet on the door, or you might find it on the radiator support under the hood.

You can look in the glove box and find the axle ratio on the information sheet on the door, or you might find it on the radiator support under the hood.

Yeah he's right...

This is what you should be at. The orange is RPM the top row shows the gear your in, then the ratio, then the MPH..

This is with 265/75/16's.

Here is what it should run with 3.55's

Here is what it should run with 4.10's

Thanks:thumbup2: by the looks of ISX's chart I have 3.55's