Fort Knox,
I think it is important to keep your truck at a more constant temperature. The thermostat is supposed to do that. If you are having problems with cooling, I would suggest the problem to be a bad thermostat, or a problem elswhere. I would want to keep the thermostat within 5 degrees from the factory recommendation (if stock). I guess that my opinion doesn't really support the "summer" thermostat. The thermostat facilitates faster warmups and makes sure that the engine temp doesn't get too cool or too hot.
Things I would do are:
1. Make sure the radiator is clean (inside and out) and water pump in good working order (check to see that belts are in good shape). Also make sure that your fan blade isn't bent or out of balance. The heater core being clogged can also contribute to poor cooling.
2. Adding a overflow tank will keep the radiator full of coolant and also help keeping things cool. Some of my trucks without an overflow will run coolant onto the ground when I have been pulling a load and then stop to get gas. If I leave the truck idle for a while, the temp will go down. Everything gets hotter under the hood because the truck stops cooling when you shut it off. The heat is basically trapped in the engine. The overflow tank will syphon the coolant back into the radiator when it cools down.
3. A fan shroud will also help direct the air through the radiator, which in turn cools more efficiently.
4. An electric fan will take less HP (less heat generated) than a belt driven fan. It also will only be on when temps go up instead of all the time. If hooked up right, the fan will also keep running after the truck is shut off (if needed), which can help with overflows as mentioned above.
5. Keep the fins of the radiator clean. Maybe when you are at the car wash, wash the radiator fins with water pressure.
6. Make sure that any radiator hoses or heater hoses have no kinks in them.
7. Keep your coolant fresh. Check your water pump to see if it needs a lubricant or not.
8. Know what cap pressure rating should be on your radiator. Talk with your radiator guy to find out what pressure cap you should run on your radiator if you don't know. I would do that in person looking at the cooling system and not by phone. If your radiator isn't in the best of shape anymore, he may suggest a lower pressure cap. Be careful about changing the pressure rating. The pressure allows the coolant temp to be higher before it reaches its boiling point. Higher pressure can also blow a hose, radiator or heater core.
All of these things will also contribute to the vehicles ability to heat in the winter also.
