2005 Other Renault Models Car looses power

Engine Performance problem
2005 Other Renault Models Two Wheel Drive Manual 35.000 miles

i have a Renault Modus 1.5 diesel, the problem is that sometimes when iam driving the car seems to loose the power and slows down and the starts speedind up again, it hapens to me mostly when iam driving up a road ( I live in a city with losts of hills) to work, but it has happened to me while driving in the highway.
i was told it could be the diesel injector and I was thinking that I should try a diesel injector cleaner that we put in the deposit with the diesel and it helps clean out but iam worried that I might make it worse, can you help me please?