overheat only over 3000 rpm

Overheating out on the highway is usually an airflow issue.

No, if it's a flow issue of any kind, it's usually a waterflow issue, because at highway speeds there's usually plenty of airflow through the rad by the forward motion of the car. But yeah, maybe not if the rad is blocked by seventeen fans, or four of them.

(Overheating at idle/low speed/stuck in traffic, now that's usually an airflow issue due to insufficient fan.)