[C-10 simplex]

For 81, The 6 cylinders got 2.73 as std axle ratio. GQ1


The 8's got 2.56 GQ1


Unless it's a california truck; In that case 6 cylinders got 3.08 as the std axle ratio code GQ1 and 8's got 2.73.

i went thru this dilema yrs ago when i first got my truck.

Also, if you bring your vin# to any decent gm dealer they can type it in and tell you exactly what gear ratio came with the truck originally.