Aoa mike786, normally Reborn does not heats up on long hilly journeys but lets not forget that most Reborn are now five years old which mean that over the years the radiators are clogged with dust, diesel and bugs and this leads to less heat transfer. And now add to that the hilly terrain which puts strain on engine and then additional load in your car as well. One more thing the air is less dense at high altitudes which means the heat transfer rate gets depreciated in simple terms less dense air flowing over your radiator coil.
I would not worry too much about it. If I were you I would take sometime out and get the radiator coil and air conditioning coil thoroughly cleaned. Its time consuming because they have to take off the front bumper but its worth the effort. Secondly I would drain the exiting coolant and replace it with Honda OEM coolant.
