Dealer should be selling synthetic cheaper than conventional oil. Not because it is, but, there is plenty of money to be made on older trucks fixing new oil leaks from switching to synthetic. New oil leaks is the biggest reason not to switch. On sale this past week Full Synthetic was 10$ a gal cheaper than conventional for family's gas engine stuff. It leaks anyway...
Synthetic doesn't mean what it used to mean. At 5K miles the fact that Shell dino oil will go a longer distance than their synthetic to satisfy Frugal fleet managers won't matter to you. (Pointed out in a past TDR issue.) More or less synthetic oil has become glorified conventional oil and conventional oil has greatly improved. Still a difference though.
If we had a real oil pressure gauge, we don't, you would notice synthetic would have higher oil pressure at hot idle in said extreme summer temps. Even with lower pressure it's still within spec so NBD other than it indicates a difference.
Corvette is a perfect example of the difference between the oils. GM Bean counter cheap and marketing getting together to save GM the cost of an oil cooler on Corvettes for some model years way back when. Conventional oil wouldn't survive oil temps experienced on the Corvette without the oil cooler, but, synthetic would. So market it as no-compromise factory fill Mobil1 and omit the expensive oil cooler. With the troublesome cheap garbage oil cooler hoses that can't take high oil temps GM is known to use you can see the pressure to leave a factory oil cooler off anyway.
In an example of "wrong tool for the job" you can even exceed synthetic oil's ability. Recall the ads for Mobil1 showing an engine town down with no wear? Towing with a 3.9 V6 using said oil and cam wiped out at ~1/4 million miles. Yeah the owner is now doing oil analysis and it's showing em how ugly the oil gets working a 3.9 V6 this damn hard in extreme temps. (You know it's working hard when the HVAC doors change position due to extended no vacuum time and very slow leak.) Yeah lasted that much longer... Amsoil in the transmission and it's fine. Rear end is being rebuilt now. Think it's close to 300K now.
https://www.turbodieselregister.com...oosing-the-battle-with-5-misfire-code.257192/
So in extreme summer temps towing, yes, you are closer to the limits of conventional oil. This by itself on a well cooled Dodge Ram Diesel doesn't matter so much. A factor also in your favor is shorter 5K oil changes. The emissions equipment holding more heat in the engine is a factor. IMO only if SHTF like a blown radiator hose or other high oil temp event and you stayed between the failure point of conventional oil, but, under the failure temp of today's so called synthetic oil would it do you any good. Again this risk is offset by repair expense of new oil leaks.
Other rides that don't have the better cooling system your Dodge Ram has may get a better benefit from synthetic use during the summer.