I own a 1991 Buick Skylark with a problem that is driving me and the mechanic nuts! My car has always been reliable until now.
Every once in awhile, out of the blue, the engine will die and won't restart until it sits for at least twenty minutes or so. The mechanics have already replaced the computer, the fuel filter, the fuel pump and the ignition module.
The best way to diagnose an intermittent problem like the one you are experiencing is to let the technician himself drive the vehicle until the fault reappears. This way he can not only feel the condition as it occurs, but he can quickly pop the hood and test for adequate spark, fuel pressure and fuel injector operation -- while the car is still dead in the water.
Another helpful tool is a portable monitoring device which attaches to the computer system. This actually records all-important data as soon as you hit the little red trigger button when you feel the engine beginning to shut down. However, this does not compare to having a technician at the scene.
Going by the shutdown symptom, and the parts that have already been replaced, I would recommend taking a serious look at the Crankshaft Position Sensor. This engine has no distributer, but uses a DIS (Direct Ignition System). This system simply uses the Crank Sensor to determine engine position and speed instead of a distributer. There is a resistance test and an AC Voltage output test that can be performed on this sensor to determine a problem.
However, it can pass the test and still be at fault when dealing with an intermittent condition. I have seen numerous examples of a sensor coming back to life as temperatures change. This may be what's happening after the twenty minute waiting period which you have described.
A poor electrical connection in any one of a number of circuits is also a possibility. As I said, the ideal scenario is to have the technician there as the circumstances arise in order to isolate the problem.