2003 Mitsubishi Shogun car hesitates on acceleration

Hi, I have a 2.5td 4d56 engine in a shogun sport (montero) on a 2003 plate, I have a problem when accelerating. When I apply the gas there seems to be a point were the car seems to hesitate when speeding up but when I put the gas pedal down fast it dosent hesitate. Another way to describe it is say I am travelling along at 30mph and cruising and take the gas off and apply it slightly it seems to jerk then grab and pull. I have recently added a power upgrade chip which works wonders and I have recently replaced the clutch, timing belts, oil filter and oil, fuel filter and air filter. Hope you can gie me an indication Thanks Ian