Intermittent check engine light

I have the vehicle listed above CXL with the all aluminum 5.3L V8 engine. The car has been maintained very well. The car normally runs very well and never gave me trouble until about 6 months ago. Intermittently, the CEL will flash on with a chime sound and the engine will stumble like it started to shut off. But before it shuts off, it recovers as if nothing ever happened. There are no current or pending error codes.
I have changed the fuel pump and fuel filter, all O2 sensors, the cam sensor, the crank sensor, the complete throttle valve with TSP as well. I installed a new alternator and heavy duty battery. I even changed the fuse and relay panel with a new one. No matter what I do the symptoms remain.
The car originally came from Canada and had an aftermarket remote start system installed. It is a "FirsTech CM-6200 with a BLADE-AL immobilizer bypass system. I thought maybe there was a problem with that system, so I unplugged and completely removed it. Interestingly, the engine still starts and runs the same even with a plain non-chipped key.