td4 power problem

I have a Freelander TD4 '04, about 120K, just had a reconditioned turbo fitted along with all the new oil pipes etc as recommended. The problem is that if its driven hard by hard I mean at 70mph for about 12mls the power falls away, NO engine management lights come up the power just drops off, a bit like safe mode but no wanrning light. Does anyone have any ideas, I would be grateful for some help, I'm totally stuck.