On our older dakotas the gear info was printed on a decal on the inside of the hood, on our newer ram pickups it is listed on a decal on the glove box door. You probably have Chrysler 9.25 differentials and the common ratio is 3.55, there sometimes is a metal tag on one of the cover bolts with the number of teeth listed, but it is often very hard to read.
Ebay has some excellent sources of new and used parts and some of the sites have a lot of helpful info, identification pictures, the 9.25 has a stopsign shaped symetrical cover for instance. There are complete and detailed instructions on dissassembly and setup available online.
You will be able to save hundreds of dollars buying your parts online, I am very happy with Riverside Gear, fast service & fair prices, but it sounds like you may need a complete assembly which is also available on Ebay.
Don't wait too long, my niece drove her chevy until the teeth were completely worn off, that added a $150 tow bill to the repair. Good luck