Ok.... couple thoughts but no real train to carry them together.
Newer motors across all makes are seeing a considerable increase in carbon build up. Thinner ringlands and rings to get better efficiency and better fuel economy are likely the cause. They are also getting thinner oil. So it all adds up increased blow by and carbon build up. It is almost required now to do some sort of carbon cleaning i.e. Seafoam, BG cleaning.
This is a running 5.7 with 80k on it
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Since you are already in that far, I would 100% say a compression test is a good idea. Also a leak down test would be wise. If for no other reason than having that peace of mind.
I never saw too many 6.4s come in with typical hemi issues compared to the 5.7, but there are so many more 5.7s out there that the numbers would be skewed even if every single motor came into the shop.