2000 Chevy Impala Can anyone help with a really tricky stal

I have a 2000 Chevy Impala with the 3.8L V6. It has nearly 160,000 miles on it but it runs strong. When it's running. The trouble is, seemingly for no reason, it stalls out. It has stalled on me at various times but usually it is when I'm slowing for a stop or under 40MPH. (Most of the time, it stalls within the first 20 minutes of driving but not always.) I've already replaced the fuel pressure regulator, the ignition module, the crank sensor, the cam sensor, the spark plug wires, the spark plugs, the fuel filter and a number of other tune up related items. I don't suspect the fuel pump because there always seems to be a strong source of fuel at the rail when I break down and I haven't stalled at highway speeds. I've cleaned the mass airflow sensor with an approved cleaning solution and examined the idle control motor which looks okay but I'm not sure how to test that under load. When the car stalls, my scanner tells me there are no engine codes or other signs that there is an engine fault. When I try to restart the car, I'm usually able to give it some gas and keep the RPMs really high while it lurches and sputters to the side of the road. I can usually do this a couple of times before I'm no longer able to force the engine to run like this. (Another indicator for me that this isn't a fuel delivery problem is the fact that I smell a lot of unburned gas when I try to restart.) Between 30 minutes and an hour later, the car will start up perfectly fine and run flawlessly for hundreds of miles or more before it suddenly dies again! Any ideas?