How to fine differential ratio
 

Where is the paper showing rear end ratio on 2013 Ram 3500? My 2001 has a paper in glove box.

Try the VIN decoder on this web site.
I have used it a few times on trucks where the metal tag located on the rear axle is missing or rusted beyond being able to read it.

In a pinch, the jack up the rear axle and spin the tires trick work pretty well. Count drive shaft rotation to tire rotations too get the #.

VINs don't have the axle ratio coded into them. What a dealer can do is lookup the build sheet using the vin as an index.

Yup - done that a time or two!

Thank you