As far as GM F-body cooling: I ran a Chevy body shop for awhile in the '90s, and whenever the lower spoiler (the 2nd one, black, behind the front cover) was broken off from parking curbs, the Camaros would overheat.
Unrelated to that, but germaine to this discussion: back at the dawn of time I had a '64 Corvair, which had quite a bit of front-end lift on the freeway. I added a 1st-gen Z28 front spoiler and that problem disappeared with no other changes.
I've added front spoilers to a few cars since, and picked up MPG or improved cooling or both, depending on the spoiler placement. The MPG was from guiding the air to the sides rather than having it bouncing off the undercarriage.
I've also vented the hood on 3 vehicles of mine through the years, which also picked up MPG & improved airflow through the engine compartment, reducing underhood temps.