Not sure what you mean by "are doing on the RAM"
Put another way. I cannot imagine constantly (15K miles) changing the gear lube on my ford as much as you do on the Ram. Last Ford F250 I had I got all hinky reading this board and yanked the diffy cover at 100K. The stuff that came out looked like new.
The F250 I have now will probably get the diffy serviced at 100K if i live to drive it that far. I go out each winter pulling a 10K fifth wheel. Since my curiosity is tweaked I am gonna get the book out of the Ford and update this post with what it says.
My Ford Scheduled maintenance service gives the following info:
Every 105K miles - Change rear axel fluid (Dana Axles)
Every 150K miles - Change the front and rear diffy and transfer case fluid.
Just saying (not trying to be anal) how does the Ram gear boxes go thru diffy oil that often when the other two of the big three do not?
:h