Highway heat

1967 dart GTS 440 car . 727 3500 stall 410 gears, alu rad dual cooling fans ( both pullers ) , engine temp runs 190-195 in town / get on highway ( 90-95 kph ) temp starts to rise after about 15 min, goes to 200-205 as soon as i get off highway temp starts to drop back again / 180 t stat in it. Had a tranny cooler hanging in front of rad ( i know tranny gets warm cause its not locking up ) re-located under car with a fan cooled unit. Doesnt matter on out side temp could be 30 c or 15 c. Any thoughts

No pics of the car in question: I knew a guy that had an unsealed hood scoop on his 505 crate motored chevy pick up that did the same thing. His scoop was bringing in enough air to combate the radiator air flow ------------