I have the Superchips FlashPaq and it does a good job. I just spent the evening installing Doug Leno's fuel rail pressure gauge. I bought the gauge because I was concerned about the boxes, programers, downloaders, etc. and what kind of fuel rail pressure increases were being applied to make more power.
It is my belief, after lot's of TDR reading, some fuel rail pressure increase might be OK, but a little more (whatever that is) or a big increase in the fuel rail pressure is just asking for trouble.
Anyway, from what I understand, the fuel rail pressure sending unit on my truck will not "record" pressure over 27,000 psi. I test drove the truck this evening, and ran it pretty hard, but did not really get to wide open throttle (it's after midnight and I really did not want any discussions with the local police department) and the fuel rail pressure did not go over about 23,000 psi.
So, after a very brief, and a not too scientific test, it looks like the Superchips does not use a lot of fuel rail pressure increase to get the power. Tomorrow, I will turn it back to stock and see what the pressure is.
I hope I answered your question.