When the car is cold it operates great. After a couple of miles it begins to behave erratically, regardless of throttle position, the car starts shaking and sputtering. I've replaced the fuel pump and sender, 02 sensor, plugs and wires, and TPS as well as the ECM and have not located any VAC leaks. Good pressures at the fuel rail and I am certain that it is not a fuel issue (though I'm sure the injectors are long due for replacement). I believe it to be a mixture problem do to a poor ECM computation from a sensor read somewhere but I can't imagine which one or perhaps a timing issue but I feel that is less likely since it runs perfectly when still cool. FYI, temp gauge never reports anything above 160 - 200 Degrees so I know it's not running hot... any thoughts?