Join Date: May 2011
Location: Frederick MD.
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A few different thoughts here.
First, I would take a temp gun and measure the temp difference at the inlet and outlet hoses of the radiator. Just curious if the thermostat is opening of correctly, or if the radiator is cooling the coolant properly.
Second, what sort of coolant are you using, and is it diluted properly? I once had a truck that someone put straight anti-freeze in. It kept overheating and it took awhile to figure out. Straight anti-freeze does not absorb heat as well as when it's diluted with water.
Third, I would install a pressure tester and see how much pressure you're building in your coolant system. If it starts building pressure and just keeps going up and up then I would suspect head gaskets.
One last thing, are you sure the water pump is working properly? Could be something as stupid as a spun impeller.
The vacuum issue is unrelated. These trucks use an electrical vacuum pump so it has nothing to do with the engine.
I'm confused with what all you've had done to the truck and when it was done. You have had head gaskets? How long ago, and were they OEM gaskets? What was the reason you did the repairs 15000 miles ago? Blown EGR cooler? Oil in the coolant?