Is it possible to have air trapped in the coolant line running to my heater core?
I just replaced my radiator and water pump, thermostat is working and everything is cooling and circulating.However I get no heat, the coolant lines running to and from the heater are cool to the touch with the exception of the few inches of hose near the water pump.
Absolutely. Typically the heater hoses are the highest point in the cooling system so if air does get in, it will float to the top. You can purge it by disconnecting the hose that DOESN'T get hot when the truck is running (after everything has cooled down). Then lower the end of the hose until coolant begins to run out. Cap the end firmly with a thumb and reconnect it.
I might suggest putting a coolant fill point in the highest hose as a more permanent fix. These are inexpensive and will allow you to purge the system if it traps air again without the PITA of disconnecting a hose. Cooling system fill points are simply a hose connector with the garden hose fitting in-line for filling and flushing. You just have to cut the highest hose at its highest point and put the fitting in line.