Why is it that after I take my car for MB service it seems sluggish after I pick it up?

I just had car in for inspection and oil change and stated repeatedly "DO NOT REFLASH ECU, DO NOT UPDATE, DO NOT LOAD NEW CODES!!!" So I pick it up and it seems sluggish. Dealer swears that they did not reprogram ECU, but I wonder.

A related question. Why does car seem more responsive first thing in the morning after sitting over night, but less responsive later in the day even after sitting for 2 or 3 hours? This seems to be the case even when it is hotter in the garage than outside.

Any insights would be appreciated. I don't think I'm imagining these problems.