Dodge - Intrepid :: 2002 - Overheating After Replacement Of Timing Belt / Water Pump?

I have a 2002 Intrepid ES with a 3.5L V-6 with 264,000 miles on it. I have recently had the timing belt and water pump changed. Three weeks later I am driving home and the temperature gauge starts climbing. This is the first time this car has ever overheated. Well, I call my buddy who is a certified mechanic and he tows the car to his shop. I have him check the water pump to make sure it hasn't prematurely failed. He tears the front of the engine down and inspects the pump. He finds nothing wrong with the pump but he discovers the timing belt tensioner has failed and it has caused the engine to jump time, I tell him to go ahead and replace the tensioner.

After he put the engine back together he started it and it ran cool while it was sitting at idle for about 45 minutes. Then he took it for a test drive and it overheated again. He checks the thermostat and finds that it has also failed; he replaces that also, still overheating. New radiator hoses, upper and lower, new radiator, new thermostat, new water pump and it still overheats. He put dye into the coolant to check for a blown head gasket and it tested negative for a blown gasket. The exhaust doesn’t smell of burning coolant or producing white smoke. My mechanic friend and I both have run out of solutions…