Aluminum heads...

The problem is not the 200 by itself. It the change over time and the ease with which the temp rises.
I would suspect the airflow through the rad has been compromised. Either the condenser fins are packed with dirt or mud, or the rad itself may also have blocked fins.
If that don't find it I would be checking the exhaust back-pressure

'Course the check-engine lite is off;right?

As to the heads eroding into the rad, I guess that must take more than 17 years cuz my rad is is still fine.