rear differential help on chevy truck?

i have a 1992 c2500 4x2. i am trying to figure out what kind of axle ratio i have on the rear diff. this is all the info i know of the truck so far. 350ci 4bolt main, auto trans. not sure if a 700 or 4l80. 14bolt plate on the diff, and it travels 2000rpm @ 70mph on the o.e. tires (gps navigation confirmed) 70 to 70 gps to speedo (i.e 1:1) anyone know what it might be?