i need help

Do you have any PI parts (intake, heads, cams)? Even a non-PI GT should put at least 300+rwhp with a blower. Obviousy there is something very wrong with your car. Hopefully someone a bit more knowledge in the area will chime in.

Well, the 174hp he is talking about is likely at the wheels. Once you figure in drivetrain loss from the engine to rear end, you do lose a certain percentage of power the engine is making before it hits the ground.

Is the car a 5 speed or auto? If it's an auto, that isn't too, too far off (a little low), but if it's a 5 speed I'd expect it to be in the mid 180 to 190 range.

7psi isn't a whole lot. You basically gained 100rwhp over stock. That's about right, seeing as a 99-04 GT will dyno 225-235rwhp through a 5 speed, and with a run of the mill Vortech S-trim kit between 7-9psi the car will make around 340-360rwhp depending on other mods.

The biggest thing you could do is a full PI swap (99-04 heads, cams, intake). That's pretty involved, but on a smaller scale you can just run the PI cams and intake on your car and see pretty good gains. You'd still have to re-tune though.

If you have a dyno graph, what does your air/fuel ratio look like? Did he say how much timing he's using? I would expect it to be a little higher, but there are still a few variables to figure out. You can definitely get a non-PI to make 300rwhp or a little better with a safe amount of boost. I'm sure if you turn it up to 9psi you would be there, or very close.

Stock NPI motors peak at about 5100 RPM and then fall off big time. More so than what your procharger can overcome. Your motor may peak at 7PSI but you are probably well past the point where the engine is productive despite your boost. You are probably at only 5 psi at your power peak. You are intercooled, your compression is only 9.2:1, and you have sufficient fuel, I say pulley down for 11-12 PSI and enjoy. But that's just me.

Auto or 5-speed?
MustangDyno or Dynojet?
And can you post a dyno sheet?

If your car is an auto, and have no more mods than 7 psi of boost and a mid-pipe back exhaust (which is all you have said you have), then your numbers really aren't all that low, especially if it was dynoed on a MustangDyno (which reads a good bit lower than a Dynojet). The NPI intake and NPI cams are EXTREMELY restrictive, especially with a blower; I can't stress this enough. PI cams and intake are said to gain 30 hp on a stock NPI car, so I'm sure you'd gain 30+ hp with those two mods. That would put you at a solid 300 rwhp; I'm making 325 on a Dynojet with a couple more intake mods, so if you are on a MustangDyno, our numbers would then [hypothetically] be about the same.