flatspots

Hi Chaps Any thoughts to why a 1.9 jtd would develop a big flat spot from 2.5k to 3k rpm :confused:

HELP!!!! Recently I suffered a Cambelt failure and after some expensive (could have been a lot worse) repairs and a full service later, there is a massive power loss and very severe flat spots. I need 3K revs to pull away otherwise it bogs down, and the same on changing up or down gears...