1997 Dodge Ram Catalytic Convertor

Ok you are getting a multiple missfire the P0300 and then you are getting cylinder number 3 and 4 as missfires. Now I must ask does this truck have a mass air flow meter? If so get some mass air flow cleaner and clean it. I do not think it is a cat as you would have a huge power loss. I think that maybe the K&N filter has been over oiled and some got on the wire for the mass air flow unit. After you clean the sensor then clear the codes (this requires a scan tool) and let me know what you find. When you replaced the cat did you replace the rear O2 sensors? Get back to me with as much info you can and let me know how it goes.

OK your truck don't have a mass air flow meter I checked. So if you have a digital multi meter or a scan tool I would like to check the crankshaft position sensor. Here is a pic let me know if you have a meter or scanner so I tell you how to test it.

Can you scanner do a live scan? If not then you will need an inexpensive digital multi meter so we can run a couple of tests. Let me know what you scanner can do.

Ok first I would like you to check the TPS with the scanner. It will give you a voltage reading. Key on engine off you should get.2 volts or more, then slowly raise the throttle and it should steadily increase to 4.5 to 5 volts, with no glitches or drops as you open the throttle. Lets start with that and then we will check the map and cranksensor next. Let me know what you find.