Determining Ratio Without Rpo

[plh140]

I have a 2004 gmc 1500 4wd. I purchased the truck with a broken rear end. the truck has a 3.73 gear ratio according to rpo in glove box. When buying from a junkyard, how can I be sure to get the correct ratio when no rpo is available? Is there a number stamped somewhere on the rear end? Any help will be greatly appreciated.

[LeoS41280]

You can count what the ratio is. You will need a helper. If it is an open diff, fix one axle so it wont turn. Turn the other axle 20 times while your helper is counting how many times the pinion turns. If the pinion turns 34+ times it is a 3.42, 37+ times 3.72,32+ times 3.23. If it is a posi trac axle, turn the axles 10 times.