Setting still, at idle on an 80°F day, how high does the coolant temp get?
Your operating temperatures are not high. The issue is why do you need to run the fans to keep it that low? The problem can be restricted air flow through the radiator - blockage by the trans cooler, plugged radiator fins, missing plastic air “ducting” leading up to the radiator. Then there the issue of reduced heat transfer due to coated/corroded surfaces exposed to coolant, or because the bottom of the radiator or th lock is filled with sludge. Finally, restricted coolant flow.
How are you measuring the coolant temp - from a PCM scanner, or from the dash gauge? Have you checked the accuracy of the two coolant temperature sensors?
Now you added info that you have a manual fan switch, in addition to reprogrammed fan on/off temps. Is that wired per Shoebox, so as to avoid a code for the fans?
You lowered the idle RPM - why? Auto trans stock programming is 550 RPM in gear. How low did you reset the target idle speed? What other programming have you changed?
When you switched from conventional coolant to Dex-Cool did you completely flush and drain (using block drains) the coolant system? Is there any evidence of brown sludge at the radiator fill neck.
Was the question about the pump suction hose collapsing clear? When the pump pulls a suction to make the water flow, a soft hose can collapse on itself and restrict coolant flow. Not about leaks or appearance.
With regard to “chemically cleaning the water jacket”, the question wasn’t about what quality water you are using. Have you ever used a chemical additive in water to fully clean and flush the cooling system? That would remove scale from the cast iron parts and hopefully purge gunk from the radiator. If not, are facilities available at auto service shops to pressure flush the complete system? At 26+ years, things can build up the prevent heat transfer, either by coating surfaces, or even blocking critical passages. Most people have lost a factory radiator at that many years due to sludge buildup. If the system wasn’t cleared of conventional coolant when the Dex-Cool was installed, it will sludge up even worse.
Is your heater core free flowing, not plugged up? Does the heater supply line still have the flow restrictor (part #13 in diagram)?