Most axles generate the vast majority of wear metals at 15K or less and from that point despite longer and longer OCIs, the wear metal generation reduces exponentially. My Ford axles have stood up to that synopsis very well, but the same cannot be said for the Dana Advantek axles under my Jeep as noted in the comparisons shown below.
With that said, I say it depends on operating conditions, axle design, oil capacity, oil type, and other factors. For your 2006 RAM, I seem to recall AAM (the manufacturer of that axle) having a rash of issues and Dodge reduced the OCI to help compensate for it.
In the end, you can hardly go wrong by changing the oil early or on a regular basis. Of course, there is cost involved and there are also some OEMs who state "lifetime fill" with zero definition as to what that may be, but on a piece of equipment that does not have a pressurized or filtered oiling system, I prefer to err on the side of prudence.