A coupler or even lack of oil won't affect boost level.

:?:

Neither of my mufflers are stock. In fact no part of the exhaust system at all is stock.

I know that. I was asking that because due to the motor'* high mileage and unknown maintenance history (or quality of maintenance). It may be possible that the supercharger'* rotor coating may have been compromised over the years. If it indeed has been then he may have lost a pound or two at WOT.

My apologies once again for misinformation. I guess my mind was recalling the days when everyone toted how well the stock exhaust flows, and used your car as an example. I cant keep track of everything. So I guess ill have to start checking my facts before opening my virtual mouth.

All right. Sorry I had not responded sooner. I replaced the coil packs to GM stock (unknown bottom color) coils, brand new, at 27X,000 miles. Still in the 70s but earlier, I had the supercharger'* coupler replaced, and I'm not sure about the coating of the rotors.

At WOT, I get a hair more than 5 PSI. This is with a K&N FWI. Also, sometimes it feels as if I'm not giving the car much gas, but the gas pedal is down all the way. Even more rarely I get power when I don't really need it. Usually, though, I have little power below 3G RPM, but above it the car accelerates pretty well. I never drove it hard before the pipe swap because that was one of the first things I had "fixed." The muffler company did the 3" upgrade after talking to my friend'* dad. At this same time, the exhaust manifold was welded. They did a good job because it doesn't smell like gas inside my car much at all, but Seafoam revealed some tiny cracks they left behind.

I've got fairly decent fuel injectors because I haven't felt any problems. They should be GM stock-ish, but they're not as old as the car. The fuel filter has probably never been changed, so I'll get right on that.

Also, considering my performance so far, could I get a 2.25" pipe with a high-flow cat and a muffler to match? I've come to believe, after reading a few posts every now and then, that even flow and some back pressure is good for low-end torque. I'm guessing there'* a reason that I haven't found someone running less than 2.5", but I figured with all my manifold cracks but with a better-than-stock flowing exhaust, it would even out.

You shouldn't be doing any performance upgrades at all until you get your issues fixed. And at those high miles, probably not at all.

5psi is at least 3psi low. You should be getting 8-9psi stock.

Unless your PCM is dumping boost for some other reason. Start looking for vacuum leaks, scan for KR, all the goodies.

Please take pics of your FWI, and tell us what your IAT'* are when driving and when idling after a long drive.

What is an IAT? Intake air temperature? I would love to gague this.

Yup, That is What IAT stands for. You can gauge it with a scanner and if you don't got one then save up for one.

I put a thermal diode directly into the intake, by the filter. I routed it out the back of the hood and through my door hinge. The outside temperature was 25c/77f. I let the engine warm up, and cruising at 40mph, the gague read 34c/93f. I had it at WOT, and the temp rose to 35c. It was the hottest at 36c, and that'* about all. Is this a good IAT?

Please use a scantool to check your actual IAT'*, and take pics of your FWI setup for us to see.