This task is not the most simple of tasks.

When you remove the radiator from the vehicle, hold it up to the sun. If you see accumulated debris in the fins, it's your task to remove same. Water from a garden hose won't cut it. Compressed air won't cut it.

The solution is the use of a commercially available condenser cleaner in conjunction with compressed air. Careful use of a pressure washer will also assist in the task, but, extreme care must be used to prevent bending any fins.

It's a very common problem with M/B radiators due to the very close passages between the fins. My SD is running warm now........nearly all the time.........even at 75° ambients..........without a/c. The culprit is surely the radiator as it has a new water pump.

The fans are never the culprit if the vehicle is at highway speeds.