I'm ready to light this car on fire. Started off with a P0300, then went to 0303,0304 and after repairs 0303. I've replaced the coils, plugs, and ran some seafoam through the tank. I can feel the misfire on idle but not much else. Also seeing a little less MPG. Was going to change the fuel filter, but it turns out that mine is in the tank. Car is a 2010 LT with 49k miles. Any suggestions?