I have had two Ford dealers check it, and two mechanics, with O2 sensors changed, new catalytic converter three years ago. A Ford mechanic friend replaced the intake manifold gasket, lower, didn't need it. My brother inspected the upper plastic intake manifold for cracks, but found none. Starts fine, but has no power, and the hotter it gets the less power it has. I really want to fix this because it is in excellent shape and loaded with 170K miles, all of which I put on. I bought it new in '96. Idles kinda rough, press the accelerator, and it just bogs down. Friends and family have thought that they have heard a vaccum leak as I drive away. Could it be the valve cover gasket kit thing I've read about? Any ideas would be greatly appreciated.