Dave,
NO NO NO NO . It is an AIR FLOW problem, your pump runs at 1.3 times engine speed so is PERFECT. At 30mph mid 90s is NOTHING to worry about with an RS500 intercooler sitting in front of your radiator. If you're that worried about it, go back to a standard Escort Cosworth one , as that is the ONLY way you will cure it .

You still haven't confirmed if you have got rid of the two stage fan set up? .