1987 Buick Riviera with strange stalling problem

I have a 1987 Buick Riviera T-Type with 21,000 miles on it and lately it has started a habit of having the engine die while I'm driving. It doesn't stumble or sputter it simply shuts off as if you turned it off. It doesn't matter whether it is at idle, accelerating, or cruising at 60 mph. The problem is very predictable, if the cars sits for 8 hours or more it will usually run fine without cutting out. The problem seems to occur when the car sits for 1 to 5 hours between driving and it almost always happens after driving approximately 2 miles. It is so predictable that I can usually guess where it will die within a couple of hundred yards. Once the car restarts, it usually runs fine and won’t cut out again until the next time it sits for a few hours and after 2 miles. Also, it will not restart unless you turn the key to the off position and then the start position (almost as if it needs to reset something) after which it usually starts right up and acts as if nothing ever happened. This car has had a history of minor electrical problems since I bought it new in 1987, mostly loose or faulty connectors and relays and both window motors have gone out (bad gears). I had to replace the Central Power Supply because of cold solder joints from the factory and the oxygen sensor and MAF sensors have also been replaced. I have checked the onboard diagnostic codes and there are no error codes for either the ECM or the BCM. I believe it is an electrical problem but I'm not sure where to look. A Buick dealer looked at it but could not find the problem even after it stalled on him.