how's the trains oil level, I had a similar problem and I fixed it by changing the regulator on the side of the transmition. I don't remember the exact name. I remember the car used to smoke when driven on the highway and then let go of the gas and then accelerate again. This was because the engine would suck the oil thrugh the bad regulator. It would also do the same thing you discribe but it would only slip a bit and then catch on.
92' 190E 2.6