What is this obsession with a "high flow" water pump, to the degree of making up imaginary, baseless reasons why one would help? I guess if a "high flow" water pump will make your socks roll up and down and give you a happy feeling, go spend money on it. But stock water pumps have done an excellent job on Slant-6 engines for many decades—up to and including some very hairy race motors.
Once more: measure and diagnose rather than guessing and spitballing, unless the object of the game is to waste as much money and time as you possibly can and still not fix the problem.
Basics, dude: when does the car (appear to) run hot? Low-speed/stuck-in-traffic? That would be an airflow issue, like radiator fins clogged with bugs and dirt. High-speed/real-hot-day? That would be a waterflow issue, like radiator tubes clogged with corrosion and gunk and/or block mudded up past the frost plugs. Low and high speed? That would likely be a faulty radiator or faulty thermostat.
But before you get to that, the first step is to
measure the coolant temperature, with a hand-held thermometer in the top tank of the radiator, with the engine running and the gauges claiming the engine's running too hot, to see if they're telling truth or lies.
And before you even get to that, maybe study up on how cooling systems work (and how they don't) with
this 5-part article.
