Check eng. light on (p0455 gross leak / no flow) engine stalls at idle, while driving, cold or hot, no rhyme or reason.

Question

Car inconsistently stalls at idle, while driving normally, or at all parts in between. Cold or Hot, Neutral or Drive, day or night, Monday thru Sunday, there's no pattern.
Pumping the gas pedal several times will get it running again if I notice it dying while driving, and when it dies it will start back up relatively quick.

Last month (Nov.) I had the following changed:

exhaust manifold,
serpentine belt,
air filter,
oil & filter,
vacuum leak repair,
coil, rotor, dist. pick up module, cap,
plug wires, plugs,
crankshaft position sensor,
dropped the gas tank to change the fuel pump module.

Next day or two check engine light on, and the stalling condition remains. It's got 111,000 miles on it, but runs pretty good with all the new work done. Just wondering what to replace next... (vehicle?)