over about 20-30mph theres more air getting pushed thru the radiator than any fan can move. you really need the fans when you're going slower than that.

a clutch fan will do 2 things; when the engines cold its not spinning the fan, and when you're moving the fan also declutches, a clutched fan can actually restrict the air flow thru the radiator at high speeds.

if your radiator turns out to be bad, see if theres a larger one