97 toyota running too hot in summer

alright guys i have a 97 tacoma and it runs perfect as long as the temp stays below 80 outside. as soon as it starts creeping above 80 my truck starts running hot. it is ok for about 30 minutes unless i start going up long hills then it quickly rises. as soon as i start to go down a hill it will start going back to normal running temp. and yes i have it full of coolant. i just put a new fan clutch on it last year so i dont think that is the problem. any suggestions would be helpful because i am lost.

thanks

Check and see if road salt has not eaten the fins out of the radiator core, greatly reducing its efficiency…