WELCOME to the forum. OK, so you say you've checked the relay. There's two relays (high & low) in the fuse box under the hood. Does the fan work on high speed? The computer controls the on/off of the fan and which speed is selected by means of sensors and your fan doesn't work above 35mph. Above that speed, the air coming in through the radiator should/does keep the water cool. Also, the number #5 (40amp green) fuse under the hood (picture below) is for both speeds of the fan, check that. Good luck.
