5.7 L, 100K miles. Bought this truck last week. Idles great, but no power. Check engine light was on, indicating bad throttle sensor and knock sensor. Replaced o2 sensor, EGR Valve, knock sensor and throttle sensor. Has new gas tank and fuel pump. replaced fuel filter. No more check engine light, but still no power. EGR solenoid checks out. Diagnostic computer doesn't find anything out of ordinary. Checked for vacuum leaks. Has new exhaust including catalytic converter on back. New distrib. cap and plug wires. Later, found leaking gasket around back side of throttle body. Replaced gasket. Still running bad. Tested fuel pressure on engine side of filter. Reads 17 PSI. Check-Engine light comes on once in a while. Code indicates engine is running lean. Any ideas what is still causing lack of power? Runs like only using half of the cylinders. Thanks in advance for the suggestions.