Strange overheat

[Rickie3]

Ok got a curly one, today was driving my 2.8 GU, traveled about 30 ks, and noticed the temp needle had shot to near high, so immediately pulled over, and found that water had been spewing out of the over flow bottle, and had sprayed all the way to the back wheel, no signs of cracked hoses or radiator, so I started her back up and filled with water into the radiator took near 2 litres, anyway I drove into the nearest town which was 2 ks away and parked it on the side of the road and left it there, as my wife had come to pick me up so I could continue to my destination. Anyway after getting back to my patrol she started with no problems,no missing no steam, so I continued to drive home, after a few hills and about 20 ks she overheated again, so pulled up and turned straight off, and from there we towed it home, my initial thoughts were cracked head or blown gasket, I removed the thermostat and that test fine, so put it back together and filled up with water again, and noticed very slight bubble now and then, and when I placed a few revs on it water was over flowing from the radiator, revs off and it stopped doing it, so I went for a 40+ K drive and not once did it overheat or blow coolant out, could I have a dodgy water pump? also when it was idling away it didnt seem like water was circulating to what I would expect it to be, or am I up for something more sinister? any advise greatly appreciated