overheating

[slumdog]

hi i have a 1.6 8 valve sporting punto it has had a new waterpump fitted,new thermostat and a new radiator its been bled coolint put in it and the temp sits ok when its idleing then it seems to overheat when you drive it oh and its had a new bottle cap put on it i dont know if its an air trap or if its the head gasket can anyone give me any ideas on what it can be thanks ...