gear ratio

If the rear gears were changed then the only way is to open up the diff and count teeth.

On a sticker in the glove box or under the hood. There is also a tag under a bolt on the diff. More than likely it is a 3.55 very few got the 3.92.

Call a dealer and give them you're VIN.

All of the truck info is posted on the sticker on the door jamb,copy it & a auto store can tell you a lot of info, coarse you can probably do it on the net also.

If your Dodge had optional gearing (like 3.92) it will be on the label in the glove compartment. If not then it will be blank.

Should be a tag on the rear axle under a bolt holding the rear diff cover on.

Thanks, will look tomorrow.

If your differential is not any kind of limited slip, you can (carefully) jack up one drive wheel, rotate the wheel exactly one revolution, count the revolutions of the driveshaft (needs a helper) and divide by two. Close approximation.

RPO codes in the glove compartment?