Still not completely clear, is the double cardan joint on all 5th gen 1500 4x4s?
Unfortunately, the Factory Service Manual is not clear on that point, nor does it state what mechanical equipment configurations will have this type joint, except for the sentence I extracted for my first response to the OP. Admittedly, it is not all that enlightening, as has been previously stated.
As a service manual, it is not very informative about the operation of things and is mostly a collection of removal and installation steps. Not at all what we inquisitive types prefer so we'll know how our vehicle works.
I don't know if mine has a double cardan joint either, but now I'm curious so going out to look at it now. But my guess is that it does not, since the transfer case and front differential are fixed in the chassis because we have independent front suspension. If the Ram had a live axle (solid axle) up front, it most likely would have this joint to eliminate the rotational velocity changes inherent with a single cardan joint (your typical universal joint).
Steve
EDIT: Just climbed under the beast and, as expected, there was no double cardan joint anywhere in my drivetrain.
I don't know if the 2500 or 3500 have a live axle up front, but if so, that's where I would expect to find one.
The universal joints I saw appeared to be the "lubed-for-life" variety, so under normal operation should not need to be serviced.
I did see the connection from transfer case to the front driveshaft was enclosed, like the CV joints at the front wheels. Whether this is to keep the joint sealed or is there to act as protection for the joint against road debris is unknown, as the FSM does not call this joint out separately from the rest.
Steve