Try locating a gear ratio tag on the front or rear covers on the axles.
Items you need to check the rear and front gear ratio.- Duct tape
- Rope, string, or ribbon.
- Flat driving surface.
On driver side tires, where the tire make contact with the flat driving surface, place a strip of duct tape.
Then place a some duct tape at one end of the rope (or ribbon, etc..., or something that will wrap around the driveshaft) and tape it to the very bottom or the very top of the driveshaft. Then drive the truck forward until the tire make one complete revolution. Then count the number of times the rope has wrapped around the driveshaft PLUS the amount the tape has rotated from where you started. For instance, If rope was taped to the very bottom of driveshaft and the rope wrapped around 3 times plus now the tape on driveshaft is facing at the very top of drive shaft (the driveshaft has turned half a turn). 3 rev plus a half turn = 3.50:1 gear ratio.