I concur with 314joey, it's just not trimmed properly, especially for that new of a hull. With older sixties flatbottoms, quite a few of the hull builders molds were designed with some "rocker" to the bottom, ( like my Stevens' hulls ), I'm guessing to soften the ride at lower speeds, I really don't know exactly, I'm sure someone with the firsthand knowledge like Harlan Orrin could tell us. I DO know that on lots of early drag boat videos porpoiseing is fairly predominant, maybe even "inherent", as you put it. There's a lot involved in bottom design, shaft angle, plate design and position, engine placement, that I'm sure comes into play,...but in the case of the boat in this video my guess is that it's just trimmed too loose.