Heater control valve

[wildwilly4x4]

Has anyone on here added a cable or vacuum actuated heater control valve to their system? I believe the lack of a control valve is causing my truck to slowly overheat in these hot summer temps when idling/driving slow with the A/C on. Heater is plumbed like stock, w/return dumping into the cold side of radiator. With no heat exchange going on in the core it is just dumping hot water into the cold side, starting a snowballing effect of hot water when the engine speed isnt up. Running an 8.1, clutch fan is good, aux. elec. fan is good. Even if it helps nothing else maybe it will help the A/C cool better. I live in the TX panhandle so there are many days that i may run the AC and heater within a few hours of each other, making a manual valve a real pain to deal with. Thanks for any suggestions!
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