P0300 Mystery MISFIRE - Difficult to Diagnose! (Intermittent "FISHBITE")

Cylinder MISFIRES are generally straight-forward to diagnose... But sometimes they're NOT! This 2008 Pontiac G5 2.2L Ecotec is setting a P0300 - Random Misfire DTC at 244k miles. It runs a bit rough at IDLE, with an OCCASIONAL "hiccup" on Cyl 4...not a constant misfire. Under LOAD, everything is smooth and PERFECT! Obviously it already has brand-new spark plugs and coils. What else could it be? Injector? Vacuum leak? Bad valve? I have to pull out ALL THE TRICKS in my diagnostic arsenal to give the customer a 100% conclusive diagnosis. Even improvise a cool exhaust TAILPIPE PRESSURE PULSE test along the way! IVAN'S PICO WAVEFORMS: https://drive.google.com/drive/folder... PHAD PRESSURE TRANSDUCER: http://www.pinehollowdiagnostics.com/... OTC 3398 Fuel INJECTION Pulse Tester: https://www.amazon.com/dp/B0002SR5OO?... TESLONG NTS500 DUAL CAMERA BORESCOPE: https://www.amazon.com/dp/B07SQ4FLYX?... THINKTOOL PROS: *****TOTAL $150 OFF!!*** https://www.amazon.com/dp/B08SWH2KP4?... Enjoy! Ivan