Did you check the owners manual?
FWIW, to me, synthetic oil and nitrogen for tires are of quite dubious benefit, and considering the cost, given a choice, I wouldn't pay the difference. Near 50 years ago I was a mechanic, I've NEVER seen an oil failure, seen plenty of lack of maintenance failures. Just keep the oil and fluids changed. 2ยข
You are aware engines have changed drastically in 50 yrs...right? Clearances, OHC, DOHC, VVT, DOD,AFM,mechanical high pressure fuel pumps, variable displacement oil pumps...the list goes on...those are all part of modern lube systems. You can mess with manufacture suggestions all you want.....I would not!
You did note synthetic is NOT required in this application, 2018 Jeep GC, 3.6? IIRC, full synthetic is only required for SRT's at this time. I think the biggest move in synthetics these days is in the 0W category. As I recall from the "old days" extreme temperature breakdown resistance was the primary benefit of full synthetics. I AM using it (5W-20) in our newer cars because the dealer quit offering semi synthetic, full synthetic is NOT required AT LEAST ACCORDING to Chrysler. MS-6395 IS required.
With that out of the way, there is a case to be made for full synthetic in the 3.6 because of failing rocker arms. Is it an oiling failure, design issue, quality issue? dunno. Early Pentastars required 5W-30, in 2013 they changed it to 5W-20. Only the first guess do we have any control over, but there's LOT's of failed 3.6 rocker arms that have ONLY been fed a diet of full synthetics, so crapshoot.
FWIW, our Hemi lifters are noisy no matter what oil they're fed.
For the cost of nitrogen, I'll go through the drill of adding air every fall.
