420 SEL Fuel Problems?

I have a 91 Mercedes 420SEL that's about to drive me crazy. I've had the entire fuel system rebuilt. Fuel tank cleaned, new fuel pumps, fuel lines, fuel distributor rebuilt, injectors cleaned, you name it. Car misses for a few seconds when started cold, then smooth's out nicely. From a standing start if I mash it hard, the engine will die. I'm not trying to be a speed demon, but I find this to be dangerous in traffc.
Any suggestions.

JD