Originally Posted by mln01

I always hate to see people throw parts at a problem without full diagnosis. You can get a loaner cooling system pressure test kit from an auto parts store. Connect it to the cooling system by replacing the coolant reservoir cap with the correct adapter from the kit. Pump the system pressure up to 20 lb and look for leaks. The leak should be evident within the first several minutes. If no leak is evident but the pressure drops check the back of each head where it mates with the block. That's where external head gasket leaks occur most frequently.

I'm surprised no one has mentioned the throttle body heater gasket as a possible source of the leak. They fail commonly. You may be able to see coolant or coolant residue under the throttle body heater. If so, replace the TBH gasket or remove the hoses from it and block them off by inserting an appropriate diameter short bolt into each hose, securing them with small hose clamps. It the TBH gasket was leaking, correct that problem and drive the truck again for a while to see if addressing that corrected the problem or if there is another leak.