It's not the Injectors. I would have to say it's the lost motion assemblies. Same problem with my friends car. We thought it was the injectors too, he bought new injectors and same problem. Months later we did the headgasket and I decide to inspect the rocker arms. I notice that the mid rocker arm sat lower than the ones on my head. I took out the lost mostion asmebly and measured the height, sure enough it was less than stock specs, bought new ones and problem solved.