Valvoline is good. For most all fluids I use Mopar products in my Mopars, and GM fluids in my GM's and VW fluids in my VW's (except for diff's). You should be able to buy the mopar fluid part number listed in your manual for your Xfer case, on Amazon/Rock-Auto, or go to a small-town dealer who may (they do around here) sell fluids out of their bulk barrels for a lot less (take your clean milk jugs). I generally get fluids from our dealer (from the barrel). Its cheaper, I get a chance to banter with the parts or service guy (for future parts discounts) ...and know I have the right stuff in the vehicle. Usually we walk around to the back room and talk local trash as we get it out of the barrel. You have to go to a small family dealer for that. You might get antifreeze too at the same time if you need to replace that. And it's probably time to flush out your older Ram's power steering system too ..get some at your local dealer all at once. Anyway, doing it like this I get the right stuff, save money, and always know what i put into each vehicle and don't have to guess down the road. Verify the dealer has the older part numbers for older vehicles before you go down...
For rear diff's, however, I've standardized on Walmart synthetic gear lube in all my vehicles since...about 1997 and have never had problems ...and have driven all my vehicles over 250k miles, some over 300k ...till about the time they've rusted out! My Ram has Walmart Synth rear diff lube and Mopar friction modifier. Turns out a lot of people use it. It's always low on inventory if you go to different Walmarts. It's made for them, they obviously don't refine it in the back of the store LOL. You'll need a tube of friction modifier.
I used to use Valvoine for years, and I've used others. If I was towing a camper across country, I'd probably be using a higher-spec rear diff lube. All the major brands are going to be good. Whatever brand you use, just make sure you record it and best practice is to not to mix brands.
Good luck.
____
