Daf 45 M Reg Fuel Issues/Power Issues?

Hey Guys, Some help please.
My M Reg Daf 45 is having some issues. After about 20min of driving she started to surge and lose power. Stopped her, fired her back up and works fine for about 2 min then nothing again.
Changed lift pump, and fuel filter. Took her out Sunday and she flew, like a new lorry. 45 min drive to the show, and then home. Half way home she went again, surging and lack of power. Manage to get home at 10mph.
I have stripped her down I have removed the electric strangle, that's not the fault, I have opened up the fuel filter and its half full. Lift pump appears to be working fine and pumping strong. Any ideas??