I've been where your at, mystery engine misfire. And you can go through a bucket of money trying to fix this sh%t too as you well know.
I have only a couple suggestion that might be useful to you as you sound like you already know your way around an engine:
-disconnect EGR hoses and plug them and drive it around for a little. If this makes a difference in the engine performance, better or worse, EGR is probably functioning. If it makes NO difference, maybe it is EGR after all.
-Back to basics - do a compression check. Testers are cheap at
. The online manuals here will tell you what the psi reading should be. If low in one or more cylinders, thats one of the problems if not the only one
-Could be a sticky valve or a valve thats worn to too tight a valve clearance. (Your shop probably never even thought to test for this problem.) I had this problem once with my old Nissan 200sx, except it only happened at startup - some valves were too tight and some were sticking. I'd try dumping Seafoam or Marvel Mystery in the oil and/or do two oil changes in a row, use 5-30 and see if this makes a difference. If it does, maybe a valve was stuck.
Another old timer's trick you can do - caution - is just briefly floor it while driving on the freeway - for about 10 or 20 seconds and back off the pedal. Do this a couple times (dont need no stinkin tickets) if they were stuck this may make them unstuck. Probably shouldnt need to do this more than once or twice though.
-if there are parts and sensors you think might be the problem, rather then run down and pay $$$ for the new one - go to your local pick a part junkyard first and pick the parts up there. Because you dont want to be paying $200 for a new sensor or something, and the problem is still there afterwards and find out they wont let you return it or something!