I don't have anything else to offer that hasn't already been suggested... other than asking about the airdam. Is it in place? Is it dangling or flopping around? It needs to be there in order to direct air up to the radiator.

One day, after not being able to avoid a retread tire in the road, my airdam was knocked around to the point where it wasn't directing air up to my radiator. I got off at the next exit 2 miles down the interstate (I40 in Greensboro, NC... late June timeframe), but my water temp climbed very quickly toward the red. It might have gone higher had I not pulled over. I ended up jury-rigging back in place with some bailing wire. Got back on the road and temps went back down to normal.

Good luck,
Marc