still will want to pull diff cover anyways,
you will never know for sure whats in there til you do,
axle may not even be original, you cant tell by looking outside of it
GM put the GQ1 ratio in yours, IE the default ratio- for the drivetrain ordered/installed in the truck,
and there almost always was an optional one available, sometimes two,
but obviously an optional one wasnt ordered/installed in yours, and instead the GQ1 one was installed,
its funny liek that... yeah
but it makes perfectly normal sense once you see/understand how the ordering available options RPO's system worked, every year for the new model years being ordered GM dealers had a book for the chevy trucks(for example) called chevy trucks specifications, listed in it were std equipment installed, and available options, model info and so forth, all the RPO codes and options costs were in there and descriptions of the options also, and what equipment came with options, and when options were or were not available(with certain engines, trannies, models, etc,)
once you have looked through a specificatioons book then you can fully understand how the RPO and std equipment and optional equipment systems worked
chevy sends you copies of pages of the original for a certain year and model when you order a resto packet from their 1 800 number,
there are different sections such as conventional and gasoline, std equipment, optional equipment, engines, transmissions, etc,
good luck