Loss of power in a Y reg Zafira 2 ltr dti

Hi all, hope someone can help me out here. I've recently had a new e.g.r. valve and manifold combination fitted along with new vacuum lines. Car initially working fine, but now experiencing loss of power on hills especially when cold. Starts every time and there is no hesitancy when the car is running on the flat or at idle. There are no warning displays on the dash board and the car will gather speed albeit rather slowly. The problem is particularly bad when engine is cold and, going uphill is a nightmare, I'm expecting the turbo charger to kick in but this can sometimes take anything up to 30 seconds before the car actually responds. I've also had new glow plugs fitted at the same time e g r valve was done. Diagnostics done after this showing no faults before I left the garage.

Any advice would be greatly appreciated

Thanks

Ian