E320 pulling back when accelerating up hill

[jdlsandy]

Hi, my e320 cdi seems as though its 'pulling back' when you put your foot on the accelerator to maintain the speed up a hill. The car has done 90000 miles and is on a '54' plate. The car has just had a new fuel injector pump fitted, so I assume its nothing to do with that. Help - Dont really want to throw much more money at the car now, so depending on the problem I might just chuck it in for something else.