Hey Robobrainiac- I've read through your post here and wanted to add something to watch for- a co-worker and fellow riding group member just experienced a catastrophic drive-train failure on his 2004 3500 Cummins truck. He was traveling from Michigan to South Dakota and in the middle of Wisconsin, at 75 MPH the front drive shaft came apart and busted the front output off the transfer case, taking out the brake lines, fuel lines and wiring harness.
Tow truck driver told him that he pulls at least 2 Dodge trucks a month off the road with this same failure. He is repairing it, but the hold up is the wire harness- no longer available from Dodge/FCA/Stellantis and used are hard to come by.
I have a 2001 2500 Cummins truck, basically, same transfer case as an 2004. Therefore, I did some research and what I found was the double-cardan joint at the transfer case is what fails. Since the front axle is turning the front drive shaft all the time the truck is moving. I found the claim is that there is an almost hidden grease Zerk on the joint, despite no Zerk's on the actual U-joints.
Now my friend's failure I am going to point at the transfer case out-put shaft bearing, for 2 months before his trip, a rebuilt front drive shaft was installed because he had his auto trans rebuilt and beefed-up. At that time the front shaft was found to have play in it.
So I would recommend to you to do a really good inspection of your front drive shaft and transfer case front out-put to hopefully avoid a similar failure.