2003 Fiat Doblo loses power up hills

Is the Engine revving when you are going up the hills. If it is your Clutch may be slipping. You can check same if you have a good Handbrake on the Car - Park it on a level surface with some free space to the rear of the Car - Apply the Handbrake fully - now put the Car in reverse and try to take off for a moment - if your Clutch is fine it will push the back of the Car upwards and back - if the Clutch is slipping the Car will rev and not put the sme pressure on to reverse.