w124 lag

[mus]

okay, so here is an odd symptom.

if i drive my w125 400e rather hard at highway speeds, its response is great the first couple times i step on the gas, but after that (say the next time I am passing) there is a noticeable lag and i have to really step on the pedal to get any response (as in, to the kick-down), after which it down-shifts and screams off. But that is annoying. Then, it may idle a bit roughly after that once I pull off and park. As soon turn off/on the ignition, its fine again and it responds normally. Which leads me to believe its not tranny or engine related but something to do with the throttle/vacum/computer, etc.

Note, I rarely drive this way, but am wondering if anyone has a guess and whether it is something BIG, or small.