I had a New Durango we took to Tennessee on a weekend trip. We were going up Lookout Mt when the clutches in the sure grip went out. But it was under warranty so the dealer repaired it. 80k is a bit premature for the ring and pinion to go out. Unless it was used for towing or hole shots..

Maybe a good local mechanic can help you out a little less costly. Rear ends can be a little tricky to repair. You may try a reputable salvage yard for a good recycled rear.