OP here......Definitely hoped this would not turn into a brand bash, but I still wanted some input, so I posted anyways. Sorry fellow Stihl lovers
Anyways....To reply to a few suggestions/comments above:
The dealer is a very knowledgeable mechanic and has the highest Stihl certification. I trust his troubleshooting. I do a lot of saw work for folks myself, so I feel his pain trying to fix an intermittent issue.
They definitely checked comp, vent function, and vac/press on the crankcase before ordering the special tool to test the M-tronic carb (which also checked out ok by the tester). They also explained the recalibration to me. I wish I had asked them to write down the procedure, but maybe you have to "clear" the processor before you can do the calibration ????
I'm not convinced that the issue is truly M-tronic related. Seems more like a basic "mechanical" carb issue (acts a lot like vapor lock). It only had one "spell" today, but that was enough for me.
Definitely going to take it back again. They're going to wear out the screws taking it apart and putting it together so many times.