Group, I have read (and heard) that the diff's in our cars require Dino Diff Fluid due to the seals in the diff are not compatible with synthetic fluid. I ran synthetic diff fluid in the 99 forever with no issues. When I got the 04, I originally put synthetic (Mobil 1) 75W90 in it. I changed it out later to put Valvoline 80W90 (Dino) in it. I keep waffling back and forth over this. In the owner's manual it clearly states this:
Axle Differential (front-rear): Mopar Hypoid Gear Lubricant (SAE 80W90). Do not use synthetic gear lubricant.