xterra 2000 temperature problem

[carlosrx7]

Hello, my xterra just pass the 100000 miles and take it to the dealer for the current tune up, just before reach the miles the xterra start to have high temperature as the gauge indicates so I suppose after the tune up the problem will be fixed, today still have the problem and no find the cause, so far this is what was already check, water pump (new), coolant, thermostat (new), fan clutch (good as dealer claim), radiator cap new, also check water circulation and looks good, the temperature goes up mostly on hills or when the car is stopped with the engine on, if temperature climbs, sometimes by accelerating the engine will drop rapidly but after a while the temp goes up again, any suggestion will be appreciated and sorry for my english...

[OffroadX]

I would suspect that the radiator fins have become partially obstructed with dirt and/or debris.