Rough Running Mercedes w210 E320 V6 petrol


I have the above-mentioned car year 2000. It is petrol v6 E320. As it stands it is running very badly, on idle it is sometimes ok but then changes do a very slight roughness. once in drive the car will move but if the accelerator pedal is fully pressed then I loos all power. 12 new spark plugs have been installed and 2 catalysts have been replaced at great expense. The car is also drinking excess fuel. Any idea what may be causing this? would a faulty transmission cause this? I woudlnt have thought so as it can be very rough idling on cold. Thius problem occoured when the suspension cup was replaced after standing for a while.