2005 dodge dakota 4.7l motor 135,000mi. couple of days ago coming home truck running rough and check engine light starts to blink. finally on highway at highway speed light stays constant. idle rough rev in park misses and slight backfire. trouble codes set p0300 and p0303. new plugs and coil pacs month ago visually checked plug and coil pack spark ok. replaced crankshaft position sensor still no good. what next o2 sensors auto part store printout possible blown head gasket. any help greatly appreciated thanks.

 

You need to properly diagnose the problem instead of replacing sensors at random. Your vehicle is experiencing a random misfire and also a misfire on cylinder #3.

Diagnosing Random Misfires: http://www.aa1car.com/random-misfire/
P0300 explained: https://www.obd-codes.com/p0300

This guy has a pretty good video which could be your issue. Maybe the plug on #3 is loose.

 

Been fighting this very exact same thing on my 05 4.7 for years. Usually it’s not enough or no boot grease on the coil pack. Pull the coil pack out and visually check the edges And inside of the boot for small cracks or Burnt spots. Once it does this I just go ahead and buy a new one and cover it with connector grease. Problem goes away after that. Might want to check the #4 also. Those are the main 2 that have caused me the most problems

 

Moved to the correct section.

 

Isolate the misfire to a specific cylinder. You have a p0303 but its best to view live misfire counter data on the scan tool. If all the misfire are accumulating on cylinder 3....and you have already swapped in a new plug and coil pack....have confirmed the misfire stayed on cylinder #3 and didn't move with the plug or coil (if you moved plug and coil to another cylinder), the next step is to do a compression test.