5.3 multiple misfire, any advice?

[OKGMC4]

2001 5.3l with cylinders 4 and 6 not firing. Engine light steady blink. No spark at the wires with timing light. I traded coils and same result. I traded out the coil banks from side to side and same result...so it can't be coils or coil harness. I've seen people suggest egr, plugged cats, bad fuel regulator and stuck injectors. I don't have egr or cats, and I assume since the no fire condition is on two cylinders and not random it can't be regulator or injector related. Leaking intake gasket could do it normally but it shouldn't cause a no spark condition. Any thoughts?