You can read my whole story in the 6.4 forum but the short version is I blew a head gasket towing over mount eagle TN. I knew better but was towing in a H&S level above stock. I had the HGs replaced at Power Stroke Help. Google them, they may be the best power stroke repair facility in the country. Tech there told me every HG they replaced on the 6.4 was on trucks with tuners. That's all I know except that the truck ran awesome with the H&S. Oh yeah, a couple months after the HGs the truck was totaled.

 

I don't think this "advancement" is unique to just H&S.

nothing is a free ...to get more power from the same cubic displacement has some risk which can be compounded by marginal cooling systems, etc.