Do you know the part number for the 2.7 radiator?
I'm having similar problems, car gets to just under 100ºC going on short uphills but cools down again on flat to around 90ºC. This is only happening in summer. I'm worried because I'm having a trip in September on the mountains which will have a lot of uphills at low speeds and I don't know if temperature is going to go past 100ºC
I changed the thermostat about 6 months ago because it was stuck open and the working temperatures were 60ºC instead of 87ºC. It works fine after that.
Another possibility is the water pump which is doing a weird noise, doesn't sound like a grinding bearing but definately sounds weird. The sound can only be heard with the engine and belt off, with the engine on it sounds completely fine.
https://www.youtube.com/shorts/SONMM14mKbw
How can I check the pump is working without taking it out? To take out the water pump you need to remove the radiator, fan, and a lot of stuff that I'm not willing to remove right now.