so does your jeep just not in the glove box. go to the front of your jeep and look staight down the front of the grill. on the left side there "should be" a little metal tag screwed to your jeep ...your build codes are on that.
but MoZ is right the easiest way to tell your gear ratio is to just look at your rear differental cover.
there will be several nubers on the tag. the first three numbers are your gear ratio.