could be a few things... lets start with MAF (mass air flow sensor) check that out. get some quick dry MAF cleaner, you might even gain horsepower doing that
That was my best guess. Another issue with the W140's is the fuel filter. Get that changed. Its not expensive and it can work wonders. You might not be getting enough fuel in your engine quick enough to ignite past 4500.
Also, get some injector cleaner.... you could have some cloged injectors.
Change your spark plugs, could also be some misfires.
change your air filters. you might not be getting enough O2 into your engine
check fuel pressure regulators. could have low fuel pressure.
finally.... your car just might be in limp mode. idk how to explain limp mode, but those are some symptomes. do some research.
Good Luck. and please reply on this post w/ whatever the problem was because my cars shifting point is 4500rpms and no sputters.