John, I felt the same way you do now when my car was experiencing several different driveability problems. The diagnosis was apparently difficult for the technician to make, and was replacing a lot of parts that didn't seem to fix the problem completely. The car was getting better in small increments, but not completely. When the technician was testing parts, I was just hoping that something would be diagnosed as bad, just so that I would have a resolution.
I threw a ton of parts at the car to fix it. More than what you have so far.
If you'd like to read my saga and have time to kill, get a hanky first to wipe the tears from your eyes.
Do a search on all the posts I've made, and go to the very first posts I've made.
I've spent a fortune on this car. More than I'd ever imagine. But at least I won the battle, and the car really does run beautifully.
2001 E430, Bourdeaux Red, Oyster interior.
1973 280SE 4.5, 170,000 miles. 568 Signal Red, Black MB Tex. "The Red Baron".