'66 Valiant Running Hotter than Expected

The '66 Valiant I recently finished went on a long interstate trip last weekend and it was rather a "cool" day for us in the low 90's. It is a 360 that has aluminum Edelbrock heads and a 4 core radiator by Bob at Glenray.. factory shroud, correct factory direct drive 7 blade fan, all lower factory grill area filler panels, and hood seal. It ran right in the middle (NOS gauge and sender) of the temp gauge till it hit 90F. After that I could modulate the temp by how fast I went.. the faster I cruised the hotter it got. Cruising around 80 MPH it got up in the 75% of the gauge. The car has AC but I have a leak to fix so I was not using it. From what I experienced I would not have been able to use it anyway. I stopped to get gas and it hit the upper normal line at the red light (about 95F outside). I was disappointed, I was sure the aluminum heads and radiator would be fine.

Now the interesting thing. On the way home at dusk through farm land there were a lot of bugs. The next morning I got them off the front of the car but when I opened the hood the BOTTOM of the hood around the fan was almost black from bug guts. The where thrown everywhere around the fan... I am scratching my head about if there is some weird aerodynamic of the '66 that causes a vacuum to first suck that many bugs up from.... ??? under the car????? and second if that is part of the cooling problem...

Anyone seen anything like this before?

Jim