overheating issue

[jimbo1812]

have just replace my 4.0 v8 for a 4.5 v8, ( the engine came from a car that had only done 29000 mile) I now have an issue with it over heating at speed, all the cooling system had been drained and the rad replaced as it had a number of cold spots. There does seem to be a miss fire on cylinder 3.

Any help that can be supply will be most greatful