Fuel Pressure

What is the fuel pressure supposed to be. My tested at 25lbs?

I've been working on an issue with my car for some time already. I have dropped from getting 28mpg to 22 mpg. I am also getting codes for misfire and running rich. After a major tune up as well as a few other repairs (with no positive results), I have just found out my fuel pressure is 43psi when the key is in the 'ON' position but then jumps up to 83psi after I start the car. When I take the vacuum line off from the Fuel Pressure Regulator while the car is running, there is no change in the fuel pressure or the performance of the car.
Does it seem like the problem is the Fuel Pressure Regulator or is there a problem elsewhere?

How would I check to see if the return line is clogged?

Do you know if there is a trick to disconnect the return line? I was trying to disconnect the line where the steel line end and changes back into rubber/plastic line. The rubber/plastic line slips over the steel line and it has 4 clips on the inside of the rubber/plastic line that clip onto the steel line. I can't seem to get all 4 clips pushed back at the same time in order to disconnect the line.

Yes there is vacuum. When the car is running and I take the vacuum line off from the regulator, there is vacuum on the vacuum line. When I remove the line there is also no change in how the car runs. I still get the same amount of pressure on the fuel rail.

I changed out my FPR earlier today and to my surprise, and disappointment, it still didn't solve my problem. I really had high hopes that this would do the trick.

With the key turned to ON, I get closer to 48psi now compared to 43psi before I changed it. After I start the car I am getting 84psi compared to the 78psi to 84psi before I changed it. I also pulled off the vacuum line with the engine running and there was no change. I was able to position the pressure gauge so I can see it from inside the car. While the car was in gear but holding down the brake, I am able to rev the engine enough so that it bogs down. The fuel pressure is still above 80psi while the engine is bogging down.

I'm not exactly sure of the mechanics behind the supercharger but it also seems that the bogging happens whenever the supercharger is giving boost according to the dashboard gauge. Could part of the problem be that the engine is getting extra fuel because of the boost but not enough air to match and is therefore dumping in way too much fuel with out enough air to back it up? Like I said, I'm not sure of the mechanics behind the S/C but I'm grasping for straws. I still don't think this would explain the reason for such high fuel pressure.

Any suggestions would be greatly appreciated.

Yes it has a S/C. It's a 99 GTP.

Shakes or Wobbles problem
1996 Pontiac Grand Prix 6 cyl Two Wheel Drive Automatic

i try to find the fuel pressure check port and cant find it the people at the shop said it was somewhere behind the engine but I cant find it I did find something on the passenger side engine look like it was at the end of the fuel rail but I wasnt sure it was under the power steering thing that you put you fluid in