Wondering..
If you put on the A/C to LO on both sides.
And just idle and idle and idle..
How hot will it get?

I had a BMW 735i which in traffic did not get too hot.
But, on the open road got hot.
This did not makes any sense.

Turns out the A/C condenser in front was plugged with airborne dirt, bugs, straw. The radiator less so - but plugged too with all that plus grease.

On my new (to me) Discovery II - I bought a can of GUNK which removes engine grime.
Sprayed it into the radiator and the A/C condenser.

Went to a self car wash and back sprayed the fins with high pressure - but not enough to bend the fins with pressure.

I did bend some fins getting the pressure hose nozzle way down in there.
Darn.

I did notice today - when I was climbing out of Boulder at 5,300 feet to Estes Park at 7,300 feet - I could hear the roar of the large fan - fan clutch had engaged and it was really pulling the air.

Thinking when you are really running hot - if you go to neutral and then to 2,000 RPM, the cooling fan should really roar and you can tell it is spinning.

I would really try to clean out junk from your A/C condenser first.
As you have a new rad, that is probably fine.