overheat only over 3000 rpm

Are you running vacuum advance? If you are not, you need to be.

If it was overheating prior to the electric fans then my best guess is the pump isn’t turning fast enough.

I always suggest a Stewart Component high flow thermostat. And a high flow water pump.

But none of that stuff does any good if the pump is turning too slow.

If I understand you correctly you are saying it’s getting hot now at a cruise. That can easily be tuning.

If prior to that it was getting hot at idle and in traffic that’s a different issue.

It sounds like you have multiple issues going on.