P0300 GMC -

Question

01 GMC SIERRA C3 6.0L AWD.Just replaced throttle position sensor,map sensor,camshaft position sensor,crankshaft sensor and knock sensor and knock sensor harness and now code P0300 pops up so I put $50 worth of 93 no ethanol and a bottle of sea foam and reset code drove it 20 miles and  light popped back on.

Answer 1

Check for exhaust back pressure, this type of engine are known for exhaust back pressure so that area should be ruled out.