why is clutch STILL slipping?

New 3 part clutch fitted, slave cyl replaced, master cyl refurbished.... clutch pedal adjusted.... so now i'm stuck as to why my pedal bitting at the top after a few miles and the clutch is slipping AGAIN... not to mention hard to change down.
The car in question Ford Mav/Nissan Terrano 2.7tdi 1997