Much of this problem is Obvious. Wrong Fan shroud.
There is NO way there should be that huge gap at edges of the blade to the shroud.
Just like Fluid dynamics and the water pump plate, the Aerodynamics of the fan shroud / blade is the same.
I am 100% sure there is air turbulence affecting the draw of the fan.
Are the temps verified with an IR gun?
You can eliminate the radiator tank trans cooler and go straight out front if you like.
A 160 T stat with give your cooling system a head start on cooling, and would be full open at a dynamic temp of around 180 on a normal working system when its hot out.
But First., Get that shroud fixed. Pontiac had RA4 cars tested in the desert with automatics for heat and cooling.
Lastly, Folks tend to use a "Recommended" A/F ratio for their injection systems. With the alcohol in fuel , Pontiacs anyway, need a richer Idle mixture to run right and stay within temp parameters.
