My truck runs too rich?

I have a problem with my truck running rich. I can smell it in the exhaust pretty bad. It has a slight miss while at idle and only idles at about 650 rpm. I have replaced both o2 sensors 3 times. A new map sensor, Idle air control valve, throttle position sensor, plugs wires, alternator, distrib. cap and rotor, new O rings on the fuels injecectors, new K&N air filter. I don't know what else to try. Nothing seems to work.