1997 Pontiac Grand Prix Stalling

The regulator is located on the engine's fuel rail near the injectors.

However you should tell me exactly how you used the gauge.

You're supposed to first do it Key on-Engine off, then Key on-Engine on.

The "Engine Off" checks your regulator, leaking injectors, or check valve at the fuel pump.

The "Engine On" checks your fuel pump, fuel filter and injectors.

You could also have a kinked fuel line, or even something simple like the gas cap is defective. (If it doesn't vent the gas tank, a vacuum will be created in the tank and the pump won't be able to push fuel through the lines)

The MAF will have nothing to do with fuel pressure. Now that you described how you tested your system pressure, I think you may have debris in your fuel system that's causing your filter/pump to remain clogged.

When your system is clogged, the pressure will build as you turn your key on, but engine off. Because the pump is running but the engine isn't using any fuel. This allows pressure to build up in the lines even with a clogged filter.

But as soon as your engine uses the fuel, the pump isn't able to push anymore fast enough past the clogged filter. So pressure drops to Zero.

This isn't the only reason why. You could have a faulty circuit also. But start with the simple things first. Remove your filter and see if it's clogged again. This will tell you that there's debris in you system (Probably rust). Then it won't make any sense to continue replacing things until you get the stuff out.

If this isn't your problem, write back and we'll go from there.