2000 Chevrolet Silverado • V8 2WD Automatic • 150,000 miles

My chevy silverado 1500 with 5.3L v8 has service engine light and p0300 (random eng misfire) and p0131 (o2 sensor- bank 1 sensor 1). The truck idles rough sometimes and at times the check engine light flashes while at an idle and idle gets even rougher. I have changed the plugs and wires, ran seafoam through the brake booster vac line, and still nothing is helping. The truck also has an extremely strong exhaust smell. Any help is greatly appreciated!
April 22, 2011.

P0300-normally caused by vacuum leak and bad fuel

Engine running rough or misfiring can be cause by the following:

1.Defective spark plugs
2.Inadequate spark/coil,defective spark plug wire.
3.Lack of compression
4.False air leakage.
5.Faulty fuel injectors.
6.Insufficient fuel pressure.
7.Contaminated fuel.
8.EGR valve that is leaking.
9.Oxygen sensors.
10.Throttle position sensor.
11.Manifold absolute pressure sensor
12.Mass Airflow Sensor
13.Idle air control valve

Note: If it doesn't apply disregard it-

Apr 22, 2011.
How can I find the vacuum leak or test to see if there is one?

Apr 22, 2011.
Listen to a hissing sound around the intake manifold/throttle body and vacuum hoses you can use a vacuum gauge

Apr 22, 2011.