thanks for the feedback....
i normally do not make it a habit to rev the engine, but there will be times (like when the engine downshifts during a passing maneuver) when the engine will need to rev, perhaps past 4500 rpms......

if it were a fuel supply problem, wouldn't it occur throughout the entire rpm range? when it was at the shop, the ignition wires were supposedly checked to see if anyone of them was bad - they were all good.

i will call the local benz dealer to see if they can tell me whether or not the car is equipped with a rev limiter.

thanks for your help