I regularly tow 2.5T and find that my coolant temp rises too, but I don't continue attacking the hill hard - I back it off, kick it down gears until the hill is done. I try to keep coolant temps below 105C.
Had a guy (towing a very similar caravan) in an Isuzu hovering around the tail of my caravan going up a hill once. I didn't pull over because I knew that mere seconds further on there was an overtaking lane. This guy roared past me obviously flogging his engine because he was in such a hurry.
Two hills later there's traffic ... and Mr Isuzu is stuck on the hill because he's overheated. I sailed past him at a whopping 30km/h.
The lesson is: slow and steady wins the race.
I should add that Mr Isuzu didn't learn from his previous lesson and caught me again just before we reached Bathurst. He was unable to pass me this time, we suspect he'd done some permanent injury to his engine.
Mine - with nearly 400,000km on the clock now - is still running smoothly.
My advice: back it off, don't push it so hard.
A tip: if you really need to go a little harder, open all of the vehicle's windows, turn the air vents to windscreen only, air conditioning compressor OFF, heat to maximum, fan to maximum. In summer (Australian summer, where air temps exceed 40C regularly) everyone inside will sweat a little but once you're at the top of the hill you can put everything back to normal.
