Hello and welcome to JA,

The fact that no code came up leads me to believe the problem is in an area that only posts a manufacturer specific code. Most generic readers will not show these. I would tend to believe it is probably in the fuel system.Fuel pressure (plugged filter, bad pump or regulator, injector pulse width, injector timing, plugged/failed injector. Of it could be a burnt valve, broken ring, blown head gasket or anything that would cause it to lose compression on a cylinder. All of these would cause a misfire and probably not set a generic OBDII code. I believe I would find some one with a reader that reads manufacturer specific codes and not continue to throw parts at it. What you have already done would have corrected 60 or 70% of misfires ( but the sensors, egr and PVC valves probably would have set a generic code) so your problem about has to be in one of the items I mentioned. I use an Auto Tap reader with manufacturer codes. I had a mid priced Ac tron and it would not display anything but the generic which has to affect emissions by 20% or so before it will set a code. If it is lack of fuel or it getting it at the wrong time, to one or more cylinders of a V8 it usually won't effect emissions but will cause it to run like crap.

Hope this helps, if so an accept would be appreciated.