1999 dodge ram van 3500 5.9 liter gas engine. Replaced plenum gasket. Ran like a top for two weeks, until I put fuel injection cleaner in it. Two days later , idle is very rough, up and down. Stalls after a min. Stalls as soon as step on peddle. Replaced IAC still no change. Replaced fuel pump assembly. No change. Not showing any codes. No vac leaks that I can find. New cap , rotor, plugs, wires. No change. Reset pcm. No change. Changed cat and muffler. No change. Anyone have any thoughts on this. Please help.