2001 Chevy Impala Hesitation under medium to heavy throttle

My Impala recently started sputtering/hesitating (like no fuel or spark) under medium to heavy throttle. If I drive with slow to medium - easy throttle around town I have no problems. About 9 mths ago I changed the spark plugs, wires, new intake gasket, fuel filter, and catalytic converter. I'm not getting any kind of check engine light when this happens.

Some suggestions are:
-catalytic converter (recently changed - shouldn't be it)
-fuel regulator
-fuel pump
-EGR (I think that was what was suggested)

So I put a fuel pressure guage on the fuel regulator and started the car. It immediately jumps to about 60psi and then starts to settle down to 44 - 46 psi (I read somewhere that it should be 46psi). The guage had a slight leak so after I turned off the engine I lost all pressure pretty quick but that could've just been the guage.

No one seems to know what it is and all of the above suggestions aren't cheap. Regulator ($90), Pump ($330).

Any ideas on what it could be or how I can narrow the issue down?