where is the rad situated? in front? does it get air force fed to it while moving down the road? if it does i would say its a different problem. going up hill at 40 should be about the same amount of air as the fan puts out. if it is not force fed, then it could be a shroud problem. i'm not sure about avaliability, but a couple of years ago you used to be able to get a product that you put in the rad. that would break loose some of the gunk... have you tried calling?