I have this problem with my 02 wrx wagon. (Flex up pipe, cat back exhaust, BOV, otherwise stock, no tune) Even at wide open throttle, it produces very little boost (negative numbers) in most gears. In 3rd and 4th, it might get up to 5-8psi but then drifts down while I am still at WOT. I am sure this topic is discussed here but I really don't know what to call it, so I can't search for it. If anyone knows what this is called, please let me know.