Ram blows *** when it comes to their oil recommendations on the diffs. It is very confusing because they say "check" every 20k miles. There is a huge difference between mineral oils and ester based fluids when it comes to the diffs.
Redline performance.
The oil just doesn't break down and also allows you to run cooler. Oil stop I believe recommends diffs change every 30k miles, and they say by using redline that doubles or triples what the recommend. There is a ton of stuff posted in the syn thread on this, more towards the front of it. I would feel very comfortable going 100k on redline in your average medium duty truck usage. Can go longer if your are basically a commuter truck, maybe less if you tow the hell out of it. Mineral oil is a crap shoot. Esters pay for themselves in the diffs, it is the most important or beneficial application where you should consider esters.