I have a 2004 Mustang GT with a 4.6 that has been having some issues lately. Started with a misfire on one of the cylinders that led me to change the coil packs. I changed all Coil packs and spark plugs at the same time, and it ran great for about a month, and started chugging and misfiring again. Took it to Ford and they said a Water leak from the thermostat gasket was causing it to spray the coil packs. Changed the thermostat, and gasket then found it leaking from the intake manifold. I completely changed the intake manifold to a brand new one, and new gaskets and cleaned and dried everything on the top end of the motor. Put it all back together, and drove it hot for a couple hours, and it is still missing, and chugging like it's holding back. I can't come across a vacuum leak anywhere, and have checked about everything I can think of...Any thoughts?