I would like to learn how to correctly identify the gear ratio for the differential in my 2500.

 

The easiest may be RPM at flat freeway speed , but not knowing what tires you have , its hard to use RPM , for that yr. the options were 3:73s & 4:10s .
I did not see a trans. in your sig. , auto/man.
Do you have stock tire size ? Or some other size ?
There should be a tag , held on by 2 bolts , hold the diff. cover on , get numbers off that .
If your going to keep the truck , you might want to get the vin. # and take to a dealer and ask for a build sheet , that will tell you anything you could want to know , unless its been modified .

 

The ring gear is stamped with the ratio. Thats the only 100% accurate way to tell.

 

notice your rpms at a certain speed while in direct (5th on a manual, drive with tc locked on an auto) and go here http://www.4lo.com/calc/gearratio.htm

 

jack the rear of the truck up mark the driveshaft and count the revolutions for one rotation of the tire, 3 1/2 turns 3.55, almost 4 turns 3.73, just over 4 turns 4.11 that should do it.

 

Thanks for all the help, Bob

 

Just look at the sticker in the glove box, it will tell you the diff. size and gearing.