Really Confused!

[Big Pappi]

Well Hello, I have an 04 Ford Expedition Eddie Bower. I keep getting a P03035 code, last time changed plug qand coil pack, bam, code came off Dash! This time it isn't working, and when I shut it down, I hear a hissing sound. Anybody got any advice?

 

[TechGuru]

Trouble Code: P0303 (4.0L V6 VIN K Auto)
Cylinder Number 3 Misfire Detected

Trouble Code: P0305 (4.0L V6 VIN K Auto)
Cylinder Number 5 Misfire Detected

Not sure which code you posted. Also you did not post which engine.