Did you just read codes or actually have it scanned to see live data?Sounds like it had a bunch of parts tossed at it.Just seeing codes isnt the same as live data stream.It could be EGR but they will usually set a code.Ive also seen where the heated O2 sensors can cause a misfire and not set a code.Thats why live data such as fuel trim,injector pulse etc is important.Rocky