I have a p0300 code on my 2006 gmc sierra with 4.8 v8. random misfire. I have changed plugs wires and all eight coils with no change. also put in can of bg fuel injection cleaner. truck runs smooth. no hesitation smooth idle. when you rev engine in neutral at 3000 rpm check engine light flashes and I get p0300 code. also at driving highway speeds under load around 70 mph it will flash also. any suggestions before I spend more money.
hook up vacuum gauge at idle
compression test on all 8 cylinders, dry and wet
hook up fuel pressure gauge at idle
fuel injector balance test
use noid lite kit to make sure all injectors are being properly pulsed