It is still going on! They still have the car, and the 'shop foreman' has driven it 'extensively' without seeing a problem. (They are looking at other things as well, and decided the rattle I complained about before requires a new rear anti-sway bar and attachments (!!??!!). )
They said after they do that I can pick up the car. I said no, it came in for the Trans under the original warranty, now expired, and if I take it back, then how will I guarantee it will be fixed under factory goodwill? I pointed out that it is intermittent, that 3 different drivers/passengers have seen it happen, and I will pick it up after it is fixed.
They said maybe it was an engine problem that made it sound like the Trans was slipping. I reminded them that the engine revved, the tach needle climbed, and the car lost momentum all at the same time, then everything 'caught' and worked normally. They said 'we rebuilt the Trans twice'. I said that was as may be, yet it still slips - maybe it is a bad Trans/torque converter, keep driving it and I will talk to you again on Friday.
I will ask MBUSA area rep and special problems tech to look at it before I take it back if it still hasn't been fixed by then. I told them to take their time, and just so there was no rush, I turned in the new E class they gave me for a loaner as I won't need a car for a while, and for their convenience I was giving back the loaner. (I prefer negotiating from any high ground I can find)
Thanks for asking!