Finally fixed the dreaded back fire on my 2002 3.9 Dakota. All the familiar symptoms.Chased all the same fixes. Got so bad the fix was to replace the intake manifold gaskets. Ran sweet----until you would put a load on it. Quick acceleration and it would still backfire through the intake. We only fixed the effect, not the cause. If you are trying everything to diagnose, think mechanical. The codes are only gonna go so far. The first diagnosis gave the code 305 which is a miss in the # 5 cylinder. We eventually took the valve cover off and realized that the # 5 exhaust valve was not opening as much as the others. We found that the factory roller on the lifter was stuck and not turning, thus rounding the cam lobe. It would lift enough that under idle or just very slight acceleration (around the neighbor hood) it would run OK but any cyclinder load with quick acceleration and there was not enough lift to unload the exhausr gases which left it no place else to go but out the intake under backfiring. A new camshaft and lifteres and the backfiring is cured. Lesson learned check to make sure the valves are all lifting. Not sure if this was a fluke or a more common problem that Dodge doesn't want to fess up too. Hope to post photos of the cam later.