Electric fan won't cool at highway speeds

Electric Fans need to be on a thermostatic control, I.E thermo-switch, to prevent turbulence that will cause air damming at cruising speed.
Try this before you switch out the fans & go back to the clutch fan. Un plug or disconnect, pull the fuse or whatever, to the electric fan & take it for a drive at highway cruising speed. (Obviously you don't want to sit in traffic or drive slowly with it like this for too long or it will overheat!) If the temps stay normal you know you need to put in a thermo-switch because the fan is causing turbulence. Also make sure it is wired correctly. If polarity is reversed you turn a "puller" into a "pusher"!