gu 2.8 getting warm

Hi all,
I will start by saying it is going to the experts next week so I guess I am not looking for the cure as that would be too hard to pin point with out looking at the car, I am looking for advice, maybe some suggestions so I can prepare for the worst or hope for the best!! LOL Anyway the basic problem is the pootrol is getting warm climbing hills or cruising above 110 Km/h, It seems to recover quite quickly when you slow down to say 90Km/h. Around town with the air con on sitting at lights ect is no problem just when you get to a high load situation. I have visually inspected the radiator and it seems to flow ok and no visible leaks, has quality coolant at the right rate in it, thermostat has been tested working. The radiator cap seems to be working IE lets some out when warm and recovers it when cooling down. The hoses all feel fine, plus they were all replaced at 100000 km (its now 125000). Has the right oil in the engine so don't think that is getting too hot. so as you can see with my limited knowledge plus lack of testing equipment It seems out of my range trying to diagnose the problem. Opps forgot to add no oil in water or visa versa. I guess it could be many things so any personal experiences would be great to hear about

Thanks in advance
Stefan