I have not read the manual directly, but I can't help but wonder if this is not one of the repeating topics about what is "recommended" versus "required" ... ???
The video link CLEARLY indicates the Hemi 6.4L truck engine was tested and developed with conventional (dino) 5w-30, and it did just fine. But they "spec" syns?
This reminds me of the debate about Corvettes and syns. Does a 'Vette "need" a syn? Well it depends ...
In competitive situations (full-on racing events such as SCCA, Auto-Cross, etc) the under-temps would cause the oil temps to get around 300F. That's hot enough to be a concern for conventional base stock oils, especially for a prolonged event. So GM specs and fills the 'Vettes with syn. But everyday conditions (such all those geriatrics you see driving their 'Vette to the country club, and even the occasional spirited light-to-light romp) do NOT cause the temps to ever come close to racing conditions. In everyday use, dino oils would more that well protect the 'Vette engine. So it's a matter of expected/planned use.
Using that logic, I have to expect that the Chrysler spec for the 6.4L Hemi "needing" syn is NOT a true "need" at all times, and probably rare, if ever. They recommend that lube as a precaution against any/all remotely possible chances you might work your engine so hard that a conventional stock might fail to do its job.
The easiest way to know this is simply to track your engine oil temps. I drive a Hemi Charger at the SO; it has a function where we can scroll through the in-dash menu to see coolant temps, oil temps, trans temp, etc. After MANY attempts to heat it up, after several minutes of emergency WOT driving and then parking at a stand still (low airflow for cooling), I've never seen any of the temps (coolant, oil, trans) go above 215F. Never.
And so this comes down to a topic I like to push, which most others ignore ... Thermal exchange rates. If your coolant/eng oil/trans oil is getting above 250F, then it is NOT, repeat NOT, the fault of the lube. It is a poor design in which the packaging of the mechanical systems has been compromised in favor of other things (space considerations, cost, etc). Why does conventional oil get too hot? Because there is not enough capacity in the system and/or the heat exchanger is too small for the application. I.E. - in the case of the Corvette, they "needed" syns because racing caused the oil to get too hot; they didn't design/install a system to keep the oil cool enough. But in "normal" driving, that never becomes a problem. OTOH - the LEO Chargers have enough cooling capacity that even with extreme pursuit driving, the temps never exceed typical expectations.
So, if your HEMI-equipped truck has the ability to tell you what your temps are, then by all means, try them in "normal" and "extreme" situations. If you never get above 250F, you will never "need" a syn. And it sounds like those two engineers from RAM have tested the trucks quite well, and their statement is that conventional 5w-30 is perfectly fine. The cooling systems are probably well designed and can manage any situation.
I will certainly give a nod to the fact that, when under warranty, there are pluses to consider in playing along with the OEM expectations. But again, is the syn a requirement, or just a recommendation? Again - there is a difference between these concepts:
- wants versus needs
- recommended versus required
YMMV.