2001 QX4

It has been 90+ degrees where I live and when idling for more than 10-15 min, the A/C stops blowing cold and is humid. Works great otherwise when ambient temps are low and car is moving. The Freon pressure is good. The Enser is old and has some dents, but has been cleaned and looks to be getting airflow. How can I tell what is wrong? Replace the radiator fan clutch? Condenser? Something else? Should also note that the engine temp gets high when on long stretches up uphill highway, but I think that is somewhat normal for an old car, no? Thanks!