1996 2.5 engine problems

Hey guys! I have a 96' dodge dakota 2.5 4 cyl. 5 speed I bought the truck in Nov and when I first got it it didnt have any problems. 2 days after i had it it left me sitting on the side of the road. Symptoms of what happened is you could feel pressure in the gas pedal and then when you give it gas it wouldnt do anything at all except sputter and backfire. It finally slowed down until you had to pull over and then once stoped it died. It took mabey five minutes to get it started back, but the whole vehichle would shake like you was trying to start out in 5th gear or something. When you give it gas it would just back fire and smother the engine. I left it sitting there and a couple of hours went back to get it and it drove home fine. When i got to looking it didnt have a catalytic converter on it. I had 1 put on and it seemed to work for awhile, then the same thing happened again. I let it sit for awhile and it started back again. This time I drove it up to Louisville for a car show and on the way home it took out in springfeild with the same problems. Only this time I only made it 20-30 mile before it took out again. I know it has to be something electrical because that is what causes backfire. Also I had a fuel pressure test done and with just the key turned on it built up to pressure and then would bleed off to 0. But if you started the engine it would hold. Is this normal? And just to add more for helpful suggestions, I had a computer check done and the code says multiple cylind missfires, missfire on cylinder #4, and fuel running to rich and then sometimes too lean. Does this mean a bad ECM? because thats some pretty funky codes. Thanks for anyone who can help!Oh and is it true if the catalytic converter was pulled off before that it would mess with to many sensors to run right again?