2008 grand Cherokee, random misfire

I have a 2008 Jeep Grand Cherokee 3.7 liter. I am getting a p0300 random misfire code. I can not figure it out for the life of me. I have changed all 02 sensors, the MAF sensor. All the plugs and coils. The converter is not clogged but the plugs are black like it is not getting enough fuel. I have 60psi at the fuel rail. I have also changed the injectors. I have searched high and low for a vacuum leak, I feel like I hear something but believe it’s just the throttle body (which i have also changed). The Jeep will idle decent when first started for about 1 minute and gradually get worse and worse until the point where it will not idle unless I am giving it gas. Does anyone have any other ideas?