Mercedes automatic transmissions have a function that will keep the engine revs high for a while to help the catalytic converters warm up quicker. Maybe this is what you are experiencing.

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"It's not about how fast you can go, but how well you can go fast."

Bob in Richmond

'97 S320 (LWB), Ruby Red Metallic, 73k miles
'97 S420V, Smoke Silver Metallic, 155k miles