Cadillac Repair: 1999 Cadillac engine stalling, light bulbs, stop signs

Question
My 99 Deville with the Northstar 4.6L engine will randomly stall when I release the gas pedal.  This used to happen only at stop signs and stop lights, but now it has started to happen even while the car is in motion.  There are no codes displayed on the dash information display, and the dealer cannot detect any codes using their analyzer.  The stalls can happen once in 6 months, or twice in a week or in one day.  The dealer is adamant that there is no known problem of this kind with this engine.
Any ideas?  I had experienced a similar problem with a 97 Deville.

Answer
I have lots of possibilities, But until it happens when it is in my hands and or the dealers mechanic, The possibilities are endless.

It's like handing you a string of the old style xmas light bulbs where when one bulb goes out intermittently the whole string of lights gose out, But you never see the intermittent bulb go out yourself. Which bulb do you replace ?.