for future in the case of not finding the sticker or on a different truck:
if the rear is open diff. ( no limited slip or locker )
Jack up one tire , either side, mark the drive shaft so you can see the mark from the tire. spin the tire 2 complete turns, while counting the turns of the driveshaft.
If the shaft makes just over 4 turns you got 4:10 s'
if it makes 3 1/2 turns you got 3:54 s'
Now for limited slip rears jack both sides of axle so both tires are off the ground. Spin the tire 1 complete turn while counting the turns of the driveshaft.
Hope this wasn't confusing
DUG