Gabriel:
Welcome to Durango ownership!!
I agree with PKU. Sounds like your oiling system is operating properly for a vehicle with that many miles.
Unless you know it has been done recently, you will want to make sure maintenance is up to date.
A good place to start is a transmission drain/refill with filter change. Since you have the 5.9 motor, you have the 46re trans behind that which also requires two band adjustments.
Once that is done, move onto the transfer case for a drain/refill. Then front and rear differentials. RP or Mobil 1 gear oil works well again here.
You will want to use OEM ATF+4 in your trans and transfer case.
Don't forget the cooling system which should be flushed and refilled based upon the type of coolant inside. This should get you started............:0)
Don