Jeff, pull the connectors off you crank and cam position sensors, I had a '94 Dodge van 318 with a bad crank sensor on it, ran like total crap....not even make it up my hill but just barely....replaced that sensor, the coil read WIDE OPEN, no continuity.....and so somehow the thing ran, I dunno...backup? limp home?? at any rate, it fixed THAT asspect of the operation....
Previous owners had a small set of maybe junkyard? injectors in it....ran really great at idle, but NO power...give it the gun and it would fall on it's ass like a ornery mule....
the backfire got me scratching my ass...I put in a old set of vette injectors....ran like a top....some jerk pulled something outta some junkyard is all I could think, not a issue in YOUR case....but it drove me krazy for a while here about 3? years ago....that and the crank sensor....which IS applicable to your shituation....
:gurney::drink: