Some might have said Pontiac lost its "excitement" with the demise of the Firebird, but in truth the division's excitation merely went back to where it started. The Grand Prix was Pontiac's signature muscle machine years before the Firebird, and became that again afterward. The car's second chance at glory came partly from its reputation, and partly from engineering, but mostly from a couple of potent V-6 engines.
The stock fuel pressure regulator on a 3.1-liter V-6 SE model was set to a maximum of 55 psi, but the system could drop as low as 48 psi with the engine running. That's the normal range for most 3800-series engines through the GM range, but the pressure regulator for the 3.8-liter in the GT model was set to open at 50 psi. Again, a 5 to 7 psi drop while running isn't uncommon. The supercharged engine used in the GTP is backward, though. It used a two-speed pump set to deliver low pressure -- 45 to 48 psi -- at idle, and pressure increased with rpm to the maximum 55 psi at higher rpm.
This "boost referencing" of fuel pressure is common practice with supercharged and turbocharged engines; the system is set up to increase fuel pressure in direct relation to supercharger boost pressure psi to ensure steady fuel delivery. Because of this, fuel pressure with the supercharged engine will vary according to how much boost the supercharger is making at any given time.
