Been a common problem for years and recently got one in the shop for the concern with the EGR port plugging up and then dumping all the egr into the one cylinder that is not plugged causing a misfire off idle. Many know of this concern but I have yet to see a good example of it. I show you some easy diagnosis before you pull the upper plenum to inspect the ports.

 

My 4.2 is misfiring badly all of a sudden, yet no CEL. I wonder if this is it.

 

It may be, if it is off idle, easy way to eliminate it just pull vac line at egr.

 

I'll try that.
Idle is not too rough, but accelerating is VERY rough and a 60 mph cruise in OD is near unbearable.