1999 ford transit 120 2.5di BT import, suffering loss of power?

Symtoms-
Extreme loss of power but not so bad when driven early in the morning possibly because of cold air temperature. Seems to hold back as if lack of fuel supply but then kicks in at high revs in each gear and takes off! when strying to climb a hill cant even get out of first gear.
Work already done, oil & filter change, fuel filter, air filter, blead fuel system. Have new injectors but not yet fitted.
Is there a air inlet temperature sensor that could be causing this problem? or any other cheap possible causes.
Have been advised to change injectors and injector pump all costly jobs. Help!