Electric fan won't cool at highway speeds

The key in the diagnosis is the statement that it cooled at speed before the conversion to an electric fan. I didn't catch if it was thermostat controlled. It might just be as simple as that. If the fans are still powered at road speed, they could just be acting like a big spinning wall. Try disconnecting them and running down the road to see what happens.

If you go back to the clutch fan, is it a standard fan (five blades)? Or, is it the HD fan for A/C cars (seven blades)? I might be wrong on the blade count, it's been awhile. That might solve your issue at traffic lights. Oh, and a fan shroud.....